Aug. 1 harvest festival with consecration of loaves, Old English hlafmæsse, literally "loaf mass," from hlaf (see loaf (n.)) + mæsse (see mass (n.2)). Altered by influence of lamb and from late 15c.-17c. occasionally spelled lambmas.
late 13c., from Old English hlaf "a portion of bread baked in a mass of definite form," from Proto-Germanic *khlaibuz, the common Germanic word for "bread" (source also of Old Norse hleifr, Swedish lev, Old Frisian hlef, Old High German hleib, German Laib, Gothic hlaifs "bread, loaf").
The Germanic root is of uncertain origin; it is perhaps connected to Old English hlifian "to raise higher, tower," on the notion of the bread rising as it bakes, but (according to OED) it is unclear whether "loaf" or "bread" is the original sense. Loaf also is disguised in lord and lady. Finnish leipä, Estonian leip, Old Church Slavonic chlebu, Lithuanian klepas probably are Germanic loan words.
The meaning "chopped meat shaped like a bread loaf" is attested from 1787. The figurative use of loaves and fishes to suggest "religious profession for the sake of personal gain" is from John vi.26.
"eucharistic service," Middle English messe, masse, from Old English mæsse, from Vulgar Latin *messa "eucharistic service," literally "dismissal," from Late Latin missa "dismissal," fem. past participle of mittere "to let go, send" (see mission).
Probably so called from the concluding words of the service, Ite, missa est, "Go, (the prayer) has been sent," or "Go, it is the dismissal." The Latin word sometimes was glossed in Old English as sendnes "send-ness." Meaning "musical setting of certain parts of the Catholic (or Anglican) liturgy" is by 1590s.
<a href="https://www.etymonline.com/word/Lammas">Etymology of Lammas by etymonline</a>
Harper, D. (n.d.). Etymology of Lammas. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Lammas