What is "for-"

For- \For-\ [AS. for-; akin to D. & G. ver-, OHG. fir-, Icel. for-, Goth. fra-, cf. Skr. par[=a]- away, Gr. ? beside, and E. far, adj. Cf. Fret to rub.] A prefix to verbs, having usually the force of a negative or privative. It often implies also loss, detriment, or destruction, and sometimes it is intensive, meaning utterly, quite thoroughly, as in forbathe.

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" (cognates: Old Norse for-, Swedish för-, Dutch ver-, Old High German fir-, German ver-); from PIE *pr-, from root *per- (1) "forward, through" (see per).\n\nIn verbs the prefix denotes

1. intensive or completive action or process, or

2. 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 Dictionary]

   \nProbably originally in Germanic with a sense of "forward, forth," but it spun out complex sense developments in the historical languages. Disused 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.

pre. 1 (context no longer productive English) Meaning "far", "away"; "from", "out" e.g. forbid, forget, forsay; forbear, fordeem. 2 (context no longer productive English) Meaning "completely", "to the fullest extent" e.g. fordo; superseded by combinations with "up" in senses where no upward movement is involved, e.g. forgive = ''give up (one's offenses)'', forgather = "gather up", forbeat = "beat up", etc. 3 (context dialectal English) very; excessively.