breakfast (n.) Look up breakfast at Dictionary.com
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."