"fertile spot in a desert, where there is a spring or well and more or less vegetation," originally in reference to the Libyan desert, 1610s, from French oasis (18c.) and directly from Late Latin oasis, from Greek oasis, probably from Hamitic (compare Coptic wahe, ouahe "oasis," properly "dwelling place," from ouih "dwell"). The same Egyptian source produced Arabic wahah. Figurative sense of "any fertile place in the midst of a waste" is by 1800.

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).

The 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. (In Middle English to sow in the flesh was "be sinful, live carnally.") Hence also feel (one's) oats "be lively," 1831, originally American English, and have/get (one's) oats "have sexual intercourse," 1923, chiefly British.

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"]

"consisting of oats or oatmeal," late 14c., oten, from oat + -en (2). Also "made of stem of the straw of oats," as shepherd's pipes were in poetry.

"Western film" (featuring horse-riding cowboys and Indians), 1946, American English, from oat, as the typical food of horses. Oats opera (on the model of soap opera) is by 1937 in U.S. slang.

Middle English oth, from Old English að "judicial swearing, solemn appeal (to deity, sacred relics, etc.), in witness of truth or a promise," from Proto-Germanic *aithaz (source also of Old Norse eiðr, Swedish ed, Old Saxon, Old Frisian eth, Middle Dutch eet, Dutch eed, German eid, Gothic aiþs "oath"), from PIE *oi-to- "an oath" (source also of Old Irish oeth "oath"). Common to Celtic and Germanic, possibly a loan-word from one to the other, but the history is obscure and it may ultimately be non-Indo-European. In reference to careless invocations of divinity, from late Old English.

"the coarsely ground meal of oats," late 14c., ote-mele, from oat + Middle English mele (see meal (n.2)).

word-forming element meaning "toward; against; before; near; across; down," also used as an intensive, from Latin ob (prep.) "in the direction of, in front of, before; toward, to, at, upon, about; in the way of; with regard to, because of," from PIE root *epi, also *opi "near, against" (see epi-).

masc. proper name, fourth of the Twelve Prophets of the Old Testament, from Hebrew Obhadyah, literally "servant of the Lord," from abhadh "he served, worshipped," related to Arabic 'abada "he served," 'abd "slave, worshipper."

"a walking about," c. 1600, from Latin obambulationem (nominative obambulatio) "a going or walking about," noun of action from past-participle stem of obambulare "to go or walk about, walk past, walk near," from ob "about" (see ob-) + ambulare "to walk, go about" (see amble (v.)).

musical instruction, used of accompaniments (especially by a single instrument, to a vocal piece), "so important that it cannot be omitted," 1724, from Italian obbligato, literally "obligated," from Latin obligatus, past participle of obligare "to bind" (see oblige). As a noun, "an accompaniment of independent importance," by 1817.