breakfast (n.)youdaoicibaDictYouDict[breakfast 词源字典]
mid-15c., from break (v.) + fast (n.). An Old English word for it was undernmete (see undern), also morgenmete "morning meal.". The verb is recorded from 1670s. Related: Breakfasted; breakfasting.

Spanish almuerzo "lunch," but formerly and still locally "breakfast," is from Latin admorsus, past participle of admordere "to bite into," from ad- "to" + mordere "to bite." In common with almuerzo, words for "breakfast" tend over time to shift in meaning toward "lunch;" compare French déjeuner "breakfast," later "lunch" (equivalent of Spanish desayuno "breakfast"), both from Vulgar Latin *disieiunare "to breakfast," from Latin dis- "apart, in a different direction from" + ieiunare, jejunare "fast" (see jejune; also compare dine). German Frühstück is from Middle High German vruostücke, literally "early bit."[breakfast etymology, breakfast origin, 英语词源]
mordant (adj.)youdaoicibaDictYouDict
late 15c., "caustic" (of words, speech), from Middle French mordant, literally "biting," present participle of mordre "to bite," from Latin mordere "to bite, bite into; nip, sting;" figuratively "to pain, cause hurt," perhaps from PIE root mer- (2) "to rub away, harm" (see smart (v.)). Related: Mordantly. The noun sense in dyeing is first recorded 1791; the adjective in this sense is from 1902. Related: Mordancy; mordantly.