1846, toast or expression wishing good health (from 16c., famously a drinking pledge by German students), Latin, literally "may it advantage (you)," third person singular present subjunctive of prodesse "to do good, be profitable" (see proud (adj.)).
Entries linking to prosit
late Old English prud, prute "excellent, splendid; arrogant, haughty, having or cherishing a high opinion of one's own merits; guilty of the sin of Pride," from Old French prud, oblique case of adjective prouz "brave, valiant" (11c., Modern French preux; compare prud'homme "brave man"), from Late Latin prode "advantageous, profitable" (source also of Italian prode "valiant"), a back-formation from Latin prodesse "be useful."
This is a compound of pro- "before, for, instead of" (from PIE root *per- (1) "forward," hence "in front of, before, first, chief") + esse "to be" (from PIE root *es- "to be"). Also see pride (n.), prowess. "The -d- in prodesse is probably due to the influence of forms like red-eo-, 'I go back,' red-imo- 'I buy back,' etc." [OED]. The Old English form with -te probably is from or influenced by pride (Old English pryto).
Meaning "elated by some act, fact, or thing" is from mid-13c. The sense of "of fearless or untamable spirit" is by c. 1400; that of "ostentatious, grand, giving reason for pride" is by mid-14c. To do (someone) proud is attested by 1819. The surname Proudfoot is attested from c. 1200 (Prudfot). A Middle English term for "drunk and belligerent" was pitcher-proud (early 15c.).
The sense of "having a high opinion of oneself," not found in Old French, might reflect the Anglo-Saxons' opinion of the Norman knights who called themselves "proud." Old Norse pruðr, either from the same French source or borrowed from Old English, had only the sense "brave, gallant, magnificent, stately" (compare Icelandic pruður, Middle Swedish prudh, Middle Danish prud).
Likewise a group of "pride" words in the Romance languages — such as French orgueil, Italian orgoglio, Spanish orgullo — are borrowings from Germanic, where they had positive senses (Old High German urgol "distinguished").
Most Indo-European languages use the same word for "proud" in its good and bad senses, but in many the bad sense seems to be the earlier one. The usual way to form the word is by some compound of terms for "over" or "high" and words for "heart," "mood," "thought," or "appearance;" such as Greek hyperephanos, literally "over-appearing;" Gothic hauhþuhts, literally "high-conscience." Old English had ofermodig "over-moody" ("mood" in Anglo-Saxon was a much more potent word than presently) and heahheort "high-heart."
Words for "proud" in other Indo-European languages sometimes reflect a physical sense of being swollen or puffed up; such as Welsh balch, probably from a root meaning "to swell," and Modern Greek kamari, from ancient Greek kamarou "furnish with a vault or arched cover," with a sense evolution via "make an arch," to "puff out the chest," to "be puffed up" (compare English slang chesty).