Etymology
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Oslo 

Norwegian capital city, a name probably based on Old Norse os "estuary, river mouth," in reference to the place's situation.

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ossicle (n.)

"a small bone; small, hard, bone-like nodule," 1570s, from Latin ossiculum, diminutive of os "bone" (from PIE root *ost- "bone").

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oscitant (adj.)

"sleepy, drowsy, sluggish," literally "yawning, gaping," 1620s, from Latin oscitans "listless, sluggish, lazy," present participle of oscitare "to gape, yawn," from os citare "to move the mouth" (see oral and cite). Related: Oscitancy.

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osculate (v.)

"to kiss (one another)," 1650s, from Latin osculatus, past participle of osculari "to kiss," from osculum "a kiss; pretty mouth, sweet mouth," literally "little mouth," diminutive of os "mouth" (see oral). Related: Osculated; osculating; osculant; osculatory.

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ossification (n.)

1690s, "the formation of bones," from Latin ossis "of bones," genitive of os "bone" (from PIE root *ost- "bone") + -fication "a making or causing." From 1705 as "a bony formation." It is recorded earlier than ossify.

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osseous (adj.)

"bony, made of bones," early 15c., ossuous, ossous, from Medieval Latin ossous, from Latin osseus "bony, of bone," from os (genitive ossis) "bone," from PIE root *ost- "bone." The word later was reformed in English (1680s), perhaps by influence of French osseux.

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ossuary (n.)

"urn or vase for the bones of the dead;" also "place where bones of the dead are deposited," 1650s, from Late Latin ossuarium "charnel house, receptacle for bones of the dead," from neuter of Latin ossuarius "of bones," from Latin os (plural ossua) "bone" (from PIE root *ost- "bone") on model of mortuarium.

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ossify (v.)

1713, intransitive, "to harden like bone, become bone;" 1721, intransitive, "convert to bone;" a back-formation from ossification, or else modeled on French ossifier (18c.) and formed from Latin os (genitive ossis) "bone" (from PIE root *ost- "bone") + -fy. Figurative sense "become rigid and fixed" (of thought, customs, etc.) is by 1858. Related: Ossified; ossifying.

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oscillation (n.)

"kind of vibration in which a body swings backward and forward," 1650s, from French oscillation and directly from Latin oscillationem (nominative oscillatio), noun of action from past-participle stem of oscillare "to swing," from oscillum "a swing," which usually is identified with the oscillum that meant "little face" (literally "little mouth"), a mask of open-mouthed Bacchus hung up in vineyards as a charm (the sense evolution would be via the notion of "swinging in the breeze"); from PIE *os- "mouth" (see oral). Figurative use, in reference to a swinging back and forth (in opinion, attitude, etc.) is by 1798.

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ossifrage (n.)

"sea-eagle, osprey," c. 1600, from Latin ossifraga "vulture," fem. of ossifragus, literally "bone-breaker," from ossifragus (adj.) "bone-breaking," from os (genitive ossis) "bone" (from PIE root *ost- "bone") + stem of frangere "to break" (from PIE root *bhreg- "to break").

By this name Pliny meant "the Lammergeier" (that name is from German and means literally "lamb-vulture"), a very large Old World vulture that swallows and digests bones and was believed also to drop them from aloft to break them and get at the marrow. But in England and France, the word was transferred to the osprey, perhaps on the basis of a rough similarity of sound between the two words.

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