haversack (n.)

"oats," Northern English, late 13c., probably from Old Norse hafre, from Proto-Germanic *habron- (source also of Old Norse hafri, Old Saxon havoro, Dutch haver, Old High German habaro, German Haber, Hafer). Buck suggests it is perhaps literally "goat-food" and compares Old Norse hafr "he-goat." "Haver is a common word in the northern countries for oats." [Johnson]

"large oblong bag," Middle English sak, from Old English sacc (West Saxon), sec (Mercian), sæc (Old Kentish) "large cloth bag," also "sackcloth," from Proto-Germanic *sakkiz (source also of Middle Dutch sak, Old High German sac, Old Norse sekkr, but Gothic sakkus probably is directly from Greek), an early borrowing from Latin saccus (also source of Old French sac, Spanish saco, Italian sacco), from Greek sakkos "bag (made of goat hair); sieve; burlap, large burlap cloak," which is from Semitic (compare Hebrew, Phoenician saq "sack, cloth of hair, bag, mourning-dress").

The wide spread of this word for "a bag" probably is due to the incident in the Biblical story of Joseph in which a sack of corn figures (Genesis xliv). In English, the meaning "a sack or sack material used as an article of clothing" as a token of penitence or mourning is from c. 1200. The baseball slang sense of "a base" is attested from 1913.

The slang meaning "bunk, bed" is by 1825, originally nautical, hence many slang phrases, originally nautical, such as sack duty "sleep;" the verb meaning "go to bed" is recorded from 1946. Sack-race (n.) is attested from 1805.

type of cereal plant, Middle English ote, from Old English ate (plural atan) "grain of the oat plant, wild oats," a word of uncertain origin, possibly from Old Norse eitill "nodule," denoting a single grain, itself of unknown origin. The English word has cognates in Frisian and some Dutch dialects. Famously defined by Johnson as, "A grain, which in England is generally given to horses, but in Scotland supports the people." Related: Oats.

The usual Germanic name is derived from Proto-Germanic *khabran (source also of Old Norse hafri, Dutch haver, source of haversack). Figurative wild oats "youthful excesses" (the notion is "crop that one will regret sowing") is attested by 1560s, in reference to the folly of sowing these instead of good grain. Hence, feel (one's) oats "be lively," 1831, originally American English.

That wilfull and vnruly age, which lacketh rypenes and discretion, and (as wee saye) hath not sowed all theyr wyeld Oates. [Thomas Newton, "Lemnie's Touchstone of complexions," 1576]

Fred: I still want to sow some wild oats!

Lamont: At your age, you don't have no wild oats, you got shredded wheat.

["Sanford and Son"]