Etymology
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for- 

prefix usually meaning "away, opposite, completely," from Old English for-, indicating loss or destruction, but in other cases completion, and used as well with intensive or pejorative force, from Proto-Germanic *fur "before, in" (source also of Old Norse for-, Swedish för-, Dutch ver-, Old High German fir-, German ver-); from PIE *pr-, from root *per- (1) "forward," hence "in front of, before, toward, near, against."

In verbs the prefix denotes (a) intensive or completive action or process, or (b) action that miscarries, turns out for the worse, results in failure, or produces adverse or opposite results. In many verbs the prefix exhibits both meanings, and the verbs frequently have secondary and figurative meanings or are synonymous with the simplex. [Middle English Compendium]

Probably originally in Germanic with a sense of "forward, forth," but it spun out complex sense developments in the historical languages. Disused as a word-forming element in Modern English. Ultimately from the same root as fore (adv.). From its use in participles it came to be an intensive prefix of adjectives in Middle English (for example Chaucer's forblak "exceedingly black"), but all these now seem to be obsolete.

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ask (v.)

Middle English asken, from Old English ascian "ask, call for an answer; make a request," earlier ahsian, from Proto-Germanic *aiskojanan (source also of Old Saxon escon, Old Frisian askia "request, demand, ask," Middle Dutch eiscen, Dutch eisen "to ask, demand," Old High German eiscon "to ask (a question)," German heischen "to ask, demand"), from PIE *ais- "to wish, desire" (source also of Sanskrit icchati "seeks, desires," Armenian aic "investigation," Old Church Slavonic iskati "to seek," Lithuanian ieškau, ieškoti "to seek").

The form in English was influenced by a Scandinavian cognate (such as Danish æske); the Old English would have evolved by normal sound changes into ash, esh, which was a Midlands and southwestern England dialect form. Modern dialectal ax is as old as Old English acsian and was an accepted literary variant until c. 1600. Related: Asked; asking.

Old English also had fregnan/frignan which carried more directly the sense of "question, inquire," and is from PIE root *prek-, the common source of words for "ask" in most Indo-European languages (see pray). If you ask me "in my opinion" is attested from 1910.

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for (prep.)

Old English for "before, in the sight of, in the presence of; as far as; during, before; on account of, for the sake of; in place of, instead of," from Proto-Germanic *fur "before; in" (source also of Old Saxon furi "before," Old Frisian for, Middle Dutch vore, Dutch voor "for, before;" German für "for;" Danish for "for," før "before;" Gothic faur "for," faura "before"), from PIE root *per- (1) "forward," hence "in front of, before," etc.

From late Old English as "in favor of." For and fore differentiated gradually in Middle English. For alone as a conjunction, "because, since, for the reason that; in order that" is from late Old English, probably a shortening of common Old English phrases such as for þon þy "therefore," literally "for the (reason) that."

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go for (v.)

1550s, "be taken or regarded as," also "be in favor of," from go (v.) + for (adv.). Meaning "attack, assail" is from 1880. Go for broke is from 1951, American English colloquial.

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tit for tat 

1550s, possibly an alteration of tip for tap "blow for blow," from tip (v.3) "tap" + tap "touch lightly." Perhaps influenced by tit (n.2).

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free-for-all (n.)

"mass brawl" (one in which all may participate), 1918, from earlier adjective use (1868), especially in reference to open horse races, American English. Earlier as a noun in reference to free-for-all horse and motorcar races.

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good-for-nothing (adj.)

"worthless," 1711, from adjectival phrase (see good (adj.)).

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demand (v.)

late 14c., demaunden, "ask questions, make inquiry," from Old French demander (12c.) "to request; to demand," from Latin demandare "entrust, charge with a commission" (in Medieval Latin, "to ask, request, demand"), from de- "completely" (see de-) + mandare "to order" (see mandate (n.)).

Meaning "ask for with insistence or urgency" is from early 15c., from Anglo-French legal use ("to ask for as a right"). Meaning "require as necessary or useful" is by 1748. Related: Demanded; demanding.

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require (v.)

late 14c., requeren, "to ask (someone) a question, inquire," a sense now obsolete, from Old French requerre, requerir "seek, procure; beg, ask, petition; demand," from Vulgar Latin *requaerere, from Latin requirere "seek to know, ask, ask for (something needed)," from re-, here perhaps meaning "repeatedly" (see re-), + quaerere "ask, seek" (see query (v.)). In some later English senses probably directly from Latin.

Still in 16c.-17c. commonly "to ask or request (to have or do something)," but this original sense of the word has been taken over by request (v.).

Also from late 14c. as "to stand in need of, want; to need for some end or purpose." The sense of "demand that (someone) do (something)" is from 1751, via the notion of "to ask for imperatively, or as a right" (late 14c.). The meaning "demand as necessary or essential on general principles" is from early 15c. Related: Required; requiring.

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inquire (v.)

c. 1300, enqueren, anqueren, "to ask (a question), ask about, ask for (specific information); learn or find out by asking, seek information or knowledge; to conduct a legal or official investigation (into an alleged offense)," from Old French enquerre "ask, inquire about" (Modern French enquérir) and directly from Medieval Latin inquerere, from in- "into" (from PIE root *en "in") + Latin quaerere "ask, seek" (see query (v.)), in place of classical Latin inquirere "seek after, search for, examine, scrutinize." The English word was respelled 14c. on the Latin model, but half-Latinized enquire persists. Related: Inquired; inquiring.

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