Etymology
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intercalate (v.)

"to insert a day into the calendar," 1610s, from Latin intercalatus, past participle of intercalare "to proclaim the insertion of an intercalary day," from inter "between" (see inter-) + calare "to call" (an intercalary day; see calendar). Sometimes used in a general sense, "to insert between others" (1824). Related: Intercalated; intercalating.

A necessary process in the Roman calendar to balance the solar and lunar aspects of it. Intercalation was done after Feb. 23 or 24 (the terminalia), every two or four years. Twenty-seven days were intercalated, making a full intercalary month (which included the last four or five days of Februarius), known as mensis intercalaris (and also known, according to Plutarch, as Mercedonius). No one now knows why the intercalation was done in the middle of February rather than after its end, unless it was because the important festivals at the end of that month (Regifugium and Equirra) were closely associated with holidays in early March. After Caesar's reform (46 B.C.E.) the only intercalary day is Feb. 29 every four years.

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ephemera (n.)

late 14c., originally a medical term, from Medieval Latin ephemera (febris) "(fever) lasting a day," from fem. of ephemerus, from Greek ephemeros "daily, for the day," also "lasting or living only one day, short-lived," from epi "on" (see epi-) + hēmerai, dative of hēmera "day," from PIE *Hehmer "day." Sense extended 17c. to short-lived insects (Modern Latin ephemera musca) and flowers; general sense of "thing of transitory existence" is first attested 1751. Compare Greek ephemeroi "men," literally "creatures of a day."

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weekday (n.)

Old English wicudæge, wucudæge "day of the week" (similar formation in Old High German wehhatag, Old Norse vikudagr). See week + day. In Middle English, any day other than Sunday.

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diurnal (adj.)

late 14c., "daily, happening every day," from Late Latin diurnalis "daily," from Latin dies "day" + -urnus, an adjectival suffix denoting time (compare hibernus "wintery"). Dies "day" is from PIE root *dyeu- "to shine" (source also of Sanskrit diva "by day," Welsh diw, Breton deiz "day;" Armenian tiw; Lithuanian diena; Old Church Slavonic dini, Polish dzień, Russian den).

From early 15c. as "performed in or occupying one day;" 1620s as "of or belonging to the daytime (as distinguished from nocturnal). Related: Diurnally.

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date (n.1)

early 14c., "a period or stretch of time, a season, an age;" mid-14c., "time when something happened or will happen," from Old French date (13c.) "date, day; time," from Medieval Latin data, noun use of fem. singular of Latin datus "given," past participle of dare "to give, grant, offer" (from PIE root *do- "to give").

From late 14c. as "the part of a writing or inscription which specifies when it was done." The sense transfer from "given" to "time" is via the Roman convention of closing every article of correspondence by writing "given" and the day and month — meaning perhaps "given to messenger" — which led to data becoming a term for "the time (and place) stated." A Roman letter would include something along the lines of datum Romae pridie Kalendas Maias — "given at Rome on the last day of April."

Out of date "no longer in vogue" is attested from c. 1600.

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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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penultimate (adj.)

"next to the last, immediately proceeding that member of a series which is the last," 1670s, from penultima (n.) on model of proximate. Earlier was penultim (mid-15c.), from Old French penultime.

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antepenultimate (adj.)

"the last but two," 1730, from antepenult (n.), 1610s, abbreviation of Latin antepænultima (syllaba) "last syllable but two in a word," from fem. of antepænultimus, from ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + pænultima, from pæne "almost" (a word of uncertain origin) + ultima "last" (see ultimate).

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lastly (adv.)

late 14c., from last (adj.) + -ly (2).

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dayside (n.)

"part of a newspaper's staff that works during the day," by 1942, American English, from day (n.) + side (n.).

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