breakfastyoudaoicibaDictYouDict[breakfast 词源字典]
breakfast: [15] Breakfast is the first food one eats in the morning, thereby literally ‘breaking’ the night’s ‘fast’. The word is first recorded in a text of 1463: ‘Expenses in breakfast, xjd’. It is a lexicalization of the phrase ‘break one’s fast’, which itself seems to have originated in the 14th century.
[breakfast etymology, breakfast origin, 英语词源]
breakfast (n.)youdaoicibaDictYouDict
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."