Etymology
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gloss (n.2)

"word inserted as an explanation, translation, or definition," c. 1300, glose (modern form from 1540s; earlier also gloze), from Late Latin glossa "obsolete or foreign word," one that requires explanation; later extended to the explanation itself, from Greek glōssa (Ionic), glōtta (Attic) "language, a tongue; word of mouth, hearsay," also "obscure or foreign word, language," also "mouthpiece," literally "the tongue" (as the organ of speech), from PIE *glogh- "thorn, point, that which is projected" (source also of Old Church Slavonic glogu "thorn," Greek glokhis "barb of an arrow").

Glosses were common in the Middle Ages, usually rendering Hebrew, Greek, or Latin words into vernacular Germanic, Celtic, or Romanic. Originally written between the lines, later in the margins. By early 14c. in a bad sense, "deceitful explanation, commentary that disguises or shifts meaning." This sense probably has been colored by gloss (n.1). Both glossology (1716) and glottology (1841) have been used in the sense "science of language."

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gloss (n.1)
"glistening smoothness, luster," 1530s, probably from Scandinavian (compare Icelandic glossi "a spark, a flame," related to glossa "to flame"), or obsolete Dutch gloos "a glowing," from Middle High German glos; probably ultimately from the same source as English glow (v.). Superficial lustrous smoothness due to the nature of the material (unlike polish, which is artificial).
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gloss (v.)
c. 1300, glosen "use fair words; speak smoothly, cajole, flatter;" late 14c. as "comment on (a text), insert a word as an explanation, interpret," from Medieval Latin glossare and Old French gloser, from Late Latin glossa (see gloss (n.2)). Modern spelling from 16c.; formerly also gloze.

The other verb, meaning "to add luster, make smooth and shining," is from 1650s, from gloss (n.1). Figurative sense of "smooth over, hide" is from 1729, mostly from the first verb, in its extended sense of "explain away, veil or shift the meaning of," but showing influence of the second. Related: Glossed; glossing.
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over- 

word-forming element meaning variously "above; highest; across; higher in power or authority; too much; above normal; outer; beyond in time, too long," from Old English ofer (from PIE root *uper "over"). Over and its Germanic relations were widely used as prefixes, and sometimes could be used with negative force. This is rare in Modern English, but compare Gothic ufarmunnon "to forget," ufar-swaran "to swear falsely;" Old English ofercræft "fraud."

In some of its uses, moreover, over is a movable element, which can be prefixed at will to almost any verb or adjective of suitable sense, as freely as an adjective can be placed before a substantive or an adverb before an adjective. [OED]

Among the old words not now existing are Old English oferlufu (Middle English oferlufe), literally "over-love," hence "excessive or immoderate love." Over- in Middle English also could carry a sense of "too little, below normal," as in over-lyght "of too little weight" (c. 1400), overlitel "too small" (mid-14c.), overshort, etc.

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over (prep., adv.)

Old English ofer "beyond; above, in place or position higher than; upon; in; across, past; more than; on high," from Proto-Germanic *uberi (source also of Old Saxon obar, Old Frisian over, Old Norse yfir, Old High German ubar, German über, Gothic ufar "over, above"), from PIE root *uper "over."

As an adjective from Old English uffera. The senses of "past, done,  finished; through the whole extent, from beginning to end" are attested from late 14c. The sense of "so as to cover the whole surface" is from c. 1400. Meaning "leaning forward and down" is from 1540s. The meaning "recovered from" is from 1929. In radio communication, it is used to indicate the speaker has finished speaking (1926).

Above expresses greater elevation, but not necessarily in or near a perpendicular direction; over expresses perpendicularity or something near it: thus, one cloud may be above another, without being over it. Over often implies motion or extension where above would not; hence the difference in sense of the flying of a bird over or above a house, the hanging of a branch over or above a wall. In such uses over seems to represent greater nearness. [Century Dictionary]

Phrase over and above (mid-15c.) is pleonastic, for emphasis. Adjective phrase over-the-counter is attested from 1875, originally of stocks and shares. To be (someone) all over "be exactly what one expects of (someone)" is by 1721.

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fly-over (n.)
also flyover, 1901 of bridges, 1931, of aircraft flights, from fly (v.1) + over (adv.).
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sleep-over (n.)
1935, from verbal phrase; see sleep (v.) + over (adv.).
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walk-over (n.)
"easy victory," 1838, such as one that happens in the absence of competitors, when the solitary starter, being obliged to complete the event, can traverse the course at a walk. Transferred sense of "anything accomplished with great ease" is attested from 1902. To walk (all) over (someone) "treat with contempt" is from 1851.
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cross-over (n.)

also crossover, 1795, a term in calico-printing, "superimposed color in the form of stripes or crossbars," from the verbal phrase; see cross (v.) + over (adv.). From 1884 in railroading; from 1912 in biology. As a general adjective from 1893; specifically of musicians and genres from 1971.

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go over (v.)
1580s, "review point by point;" see go (v.) + over (adv.). Meaning "be successful" is from 1923.
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