Etymology
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lag (n.)

in the mechanical sense "retardation of movement," 1855, from lag (v.). Also noted in Farmer and Henley ("Slang and Its Analogues") as American theatrical slang for "a wait," with an attestation from 1847. First record of lag time is from 1951.

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lag (v.)
"move slowly, fail to keep pace," 1520s, earlier as a noun meaning "last person" (1510s), later also as an adjective, "slow, tardy, coming behind" (1550s, as in lag-mon "last man"). All are of uncertain relationship and origin, possibly from a Scandinavian source (compare Norwegian lagga "go slowly"), or some dialectal version of last, lack, or delay. Related: Lag; lagging.
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time (v.)
Old English getimian "to happen, befall," from time (n.). Meaning "to appoint a time" (of an action, etc.) is attested from c. 1300; sense of "to measure or record the time of" (a race, event, etc.) is first attested 1660s. Related: Timed; timing.
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time (n.)

Old English tima "limited space of time," from Proto-Germanic *timon- "time" (source also of Old Norse timi "time, proper time," Swedish timme "an hour"), from PIE *di-mon-, suffixed form of root *da- "to divide."

Abstract sense of "time as an indefinite continuous duration" is recorded from late 14c. Personified at least since 1509 as an aged bald man (but with a forelock) carrying a scythe and an hour-glass. In English, a single word encompasses time as "extent" and "point" (French temps/fois, German zeit/mal) as well as "hour" (as in "what time is it?" compare French heure, German Uhr). Extended senses such as "occasion," "the right time," "leisure," or times (v.) "multiplied by" developed in Old and Middle English, probably as a natural outgrowth of such phrases as "He commends her a hundred times to God" (Old French La comande a Deu cent foiz).

to have a good time ( = a time of enjoyment) was common in Eng. from c 1520 to c 1688; it was app. retained in America, whence readopted in Britain in 19th c. [OED]

Time of day (now mainly preserved in negation, i.e. what someone won't give you if he doesn't like you) was a popular 17c. salutation (as in "Good time of day vnto your Royall Grace," "Richard III," I.iii.18), hence to give (one) the time of day "greet socially" (1590s); earlier was give good day (mid-14c.). The times "the current age" is from 1590s. Behind the times "old-fashioned" is recorded from 1831. Times as the name of a newspaper dates from 1788.

Time warp first attested 1954; time-traveling in the science fiction sense first recorded 1895 in H.G. Wells' "The Time Machine." Time capsule first recorded 1938, in reference to the one "deemed capable of resisting the effects of time for five thousand years preserving an account of universal achievements embedded in the grounds of the New York World's fair."

Jones [archaeologist of A.D. 5139] potters about for a while in the region which we have come to regard as New York, finds countless ruins, but little of interest to the historian except a calcified direction sheet to something called a "Time Capsule." Jones finds the capsule but cannot open it, and decides, after considerable prying at the lid, that it is merely evidence of an archaic tribal ceremony called a "publicity gag" of which he has already found many examples. [Princeton Alumni Weekly, April 14, 1939]

To do time "serve a prison sentence" is from 1865. Time frame is attested by 1964; time-limit is from 1880. About time, ironically for "long past due time," is recorded from 1920. To be on time is by 1854 in railroading.

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*g(a)lag- 
also *g(a)lakt-, Proto-Indo-European root meaning "milk."

It forms all or part of: ablactation; cafe au lait; galactic; galaxy; lactate (v.); lactate (n.); lactation; lacteal; lactescence; lactic; lactivorous; lacto-; lactose; latte; lettuce.

It is the hypothetical source of/evidence for its existence is provided by: Latin lac (genitive lactis) "milk;" Greek gala (genitive galaktos), "milk;" Armenian dialectal kaxc' "milk." The initial "g" probably was lost in Latin by dissimilation. This and the separate root *melg-, account for words for "milk" in most of the Indo-European languages. The absence of a common word for it is considered a mystery.
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jet lag (n.)
also jetlag, 1966, from jet (n.1) in the "airplane" sense + lag (n.). Also known in early days as time zone syndrome.
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time-sharing (n.)
1953, as a computing term, from time (n.) + verbal noun from share (v.). In real estate, as an arrangement in property use, it is recorded from 1976.
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good-time (adj.)
1928, from the noun phrase, from good (adj.) + time (n.). Expression to have a good time "enjoy oneself" attested from 1822; earlier have a good time of it (1771). To make good time "go fast" is from 1838. In Middle English, good time was "prosperous time," also "high time" (that something be done).
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time-span (n.)
also timespan, 1897, from time (n.) + span (n.1).
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small-time (adj.)
1910, originally theater slang for lower-salaried circuits, or ones requiring more daily performances; from noun phrase (also 1910). Compare big time.
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