Now updated for CSW19. New words, if any, and new inflections of existing words, are shown in red.
| aeon eon | the largest division of geological time, composed of several ERAS. |
| aeonian eonian | lasting for aeons, eternal. |
| aeonic | lasting an AEON. N.B. no EONIC*. |
| age | a long but indefinite period of time; any great division of world, human, or individual history; (verb) to grow older. |
| agelong | lasting for an age or very long time. |
| ahemeral | not lasting a full twenty-four hours. |
| allnight | of light, fuel, food etc.: provided for the whole night. |
| awee | awhile. |
| awhile | for a while. |
| bimester | a period of two months. |
| bimillenary | a span of 2,000 years; a 2,000th anniversary. |
| bimillennium | a period of two thousand years > BIMILLENNIUMS or BIMILLENNIA. |
| calpa kalpa | one of the Brahmanic eons, a period of 4,320,000,000 years. At the end of each calpa the world is annihilated, which is bad luck if you happen to be around at the time. |
| century | one hundred years. |
| chiliad | a group of 1000; a period of 1000 years, a MILLENNIUM. [Gk. kilioi, thousand]. |
| chiliadal chiliadic | relating to a CHILIAD. |
| chronon | a very small unit of time, defined as a) the time required for a photon to travel the diameter of an electron or b) the time between pressing one's clock in Scrabble and seeing that there was a better move you could have played. |
| coeternal | equally eternal, jointly eternal. |
| coeternally | (adv.) COETERNAL, equally eternal. |
| day | a period of twenty four hours, or period of daylight. |
| daylong | lasting all day. |
| decade | a period of ten years. |
| decennium | a period of ten years > DECENNIA or DECENNIUMS. |
| diel | a full 24-hour day > DIELS. |
| diuturnal | of long continuance; lasting. |
| downtime | the period of time when e.g. a machine is out of action. |
| eon | see AEON. |
| eonian | see AEONIAN. |
| epact | the moon's age at the beginning of the year; the excess of the calendar month or solar year over the lunar. |
| ephemeral | existing only for a day, or short period; (noun) a creature, such as a mayfly, that lives for one day only. |
| epoch epocha | a division of geologic time shorter than a PERIOD. |
| epochal | belonging to an EPOCH; of the nature of an EPOCH. |
| epochally | (adv.) EPOCHAL, belonging to an epoch. |
| era | an age; a main division of geological time. |
| eternal | something lasting forever. |
| eternalise eternalize | to make eternal. |
| eternality | the state of being eternal. |
| eternally | (adv.) ETERNAL, lasting forever. |
| eterne | eternal. |
| eternity | duration without beginning or end. |
| evanescent | fleeting, transitory. |
| evanescence | the state of being EVANESCENT. |
| everlasting | lasting forever; (noun) a flower (of Helichrysum, Antennaria or other genus) that may be kept for years without much change of appearance. |
| everlastingness | the state of being EVERLASTING. |
| evermore | for all time to come. |
| eviternal | eternal. |
| eviternally | (adv.) EVITERNAL, eternal. |
| eyeblink | a very short instant of time. |
| femtosecond | one quadrillionth part of a second. |
| forever | (noun) eternity. |
| forevermore | forever. |
| fortnight | a period of two weeks. |
| fugacious | lasting a short time, evanescent. |
| fugacity fugaciousness | the state of being FUGACIOUS. |
| gliffing | the time required to give a glance, an instant. N.B. there is a noun GLIFF, but no GLIFFED*. |
| hebdomad | a set of seven, a period of seven days. |
| henceforward | from this time on. |
| hereafter | from this time on. |
| hexaemeron | the (biblical) six days of creation. |
| hexaemeric | relating to a HEXAEMERON. |
| horal | pertaining to hour(s); hourly. |
| horary | pertaining to an hour; continuing for an hour; hourly. |
| hour | sixty minutes. |
| hourlong | lasting an hour. |
| howre | (arch.) an hour. |
| instant | a very short period of time. |
| interregnum | the time during which a throne is vacant between two reigns; a lapse in a continuous series. |
| intraday | occurring within a single day. |
| jiff jiffy | an instant. |
| jour | a day, as in jour de feste. |
| kalpa | see CALPA. |
| laytime | the total time allowed for the loading and unloading of cargo. |
| lifelong | lasting the duration of a life. |
| lifespan | the length of a life. |
| lifetime | the length of a life. |
| longtime | enduring for a long time, e.g. my longtime friend. |
| lunation | a lunar month; the interval between successive new moons. |
| lustrum | a purification of the whole Roman people made in ancient times after the census every five years; by extension a period of five years, a QUINQUENNIUM > LUSTRA or LUSTRUMS. |
| meantime meanwhile | (noun) a period of time while something else is going on. |
| mensual | pertaining to a month; monthly. |
| microsecond | one millionth of a second. |
| millennium | a period of one thousand years > MILLENNIA or MILLENNIUMS. |
| millisecond | a thousandth part of a second. |
| minute | sixty seconds; (adj.) small > MINUTER, MINUTEST. |
| mo | a moment > MOS. |
| moment | a very short period of time. |
| momentany | momentary. |
| momentariness | the state of being momentary. |
| momentary | lasting for a moment. |
| momently | for a moment. |
| moneth | a month. |
| month | one of the twelve conventional divisions of the year, or its length. |
| monthlong | lasting for a month. |
| multiday | lasting for more than one day. |
| multiyear | lasting many years. |
| nanosecond | a billionth of a second. |
| nightlong | lasting all night. |
| noughties | the decade from 2000 to 2009. |
| nychthemeral | of or relating to a NYCHTHEMERON or 24-hour period. |
| nychthemeron | a full period of a day and night: 24 hours. |
| ouk oulk | (Scots) a week. |
| period | one of the main divisions of geological time; (verb) to come or bring to an end. |
| permanent | remaining, or intended to remain, indefinitely; (noun) a permanent member of staff. |
| permanence permanency | the fact or state of being permanent. |
| permanently | (adv.) PERMANENT. |
| picosecond | a millionth of a second. |
| protense | an extension in time, a duration. |
| quadrennium | a period of four years > QUADRENNIA or QUADRENNIUMS. |
| quadriennium | a period of four years > QUADRIENNIA or QUADRIENNIUMS. |
| quinquennium | a period of five years > QUINQUENNIA or QUINQUENNIUMS. |
| saeculum seculum | an astronomical or geological age > SAECULUMS, SECULUMS or SECULA. |
| saronic | relating to a SAROS, q.v. |
| saros | a cycle of 6585.32 days in which eclipses of the sun and moon occur in same sequence and at the same intervals as in the previous such cycle. [Gk. saros, from Babylonian sharu 3600]. |
| season | one of the four natural divisions of the year, spring, summer, autumn and winter; a limited period. |
| second | the SI unit of time (symbol s), defined in terms of the resonance vibration of the caesium-133 atom as the interval occupied by a specific number of cycles. |
| seculum | see SAECULUM. |
| semester | a period of six months; especially, a term in a college or university which divides the year into two terms. [L. semestris, from sex, six + mensis, a month]. |
| sempiternal | of never-ending duration, eternal. |
| sennight | the space of seven nights and days, a week. [OE seofon nihta, from seofon, seven + nihta, plural of niht, night]. |
| septennate | a period of seven years; as, the septennate during which the President of the French Republic holds office. |
| septennium | a period of seven years > SEPTENNIA. |
| sexcentenary | relating to the number 600 or a period of 600 years. |
| somewhile | once; for a time. |
| subepoch | a subdivision of an EPOCH. |
| subperiod | part of a PERIOD. |
| svedberg | a unit of time used to measure sedimentation velocity. [From Theo Svedberg, Swedish chemist]. |
| tarnal | (coll.) eternal > TARNALLY. |
| temporary | lasting for a time only; not permanent. |
| temporariness | the state of being TEMPORARY. |
| termtime | a period during which pupils are attending school. |
| timeframe | a limited or restricted period of time. |
| timescale | the period within which something happens or is to happen. |
| towmon towmond towmont | a twelvemonth. |
| transient | not lasting long; (noun) a transient thing or being. |
| transientness | the state of being TRANSIENT. |
| transitoriness | the state of being TRANSITORY. |
| transitory | not lasting long. |
| trice | a very short time; (verb) to haul and make fast. |
| triduan | lasting three DAYS. |
| triennium | a period of three years > TRIENNIA or TRIENNIUMS. |
| trimester | a period of three months, an academic term. |
| trimestrial trimestral | relating to a TRIMESTER. |
| twelvemonth | a period of twelve months. |
| uptime | the time during which machinery is functioning. |
| week | a period of seven days. |
| weeklong | lasting for a week. |
| while | an indefinite period of time. |
| whilere | while. |
| workaday | suitable for a work day, plain and practical; (noun) a working day. |
| workweek | the working week. |
| year | the time taken by the earth to orbit the sun. |
| yearlong | lasting a year. |
| yonks | ages, a long time. N.B. no YONK*. |
| zeptosecond | a 10 to the -21 part of a second. |