1550s (implied in sneakish), "creep or steal about privately; move or go in a stealthy, slinking way" (intransitive); perhaps from some dialectal survival of Middle English sniken "to creep, crawl" (c. 1200), which is from Old English snican "to sneak along, creep, crawl," from Proto-Germanic *sneikanan, which is related to the root of snail and snake (n.).

The transitive sense of "insert stealthily" is by 1640s. That of "partake of or get surreptitiously" is from 1883. Related: Sneaking. To sneak up on someone or something is by 1869.

As an adjective, in reference to feelings, suspicions, etc., "not openly vowed, undemonstrative," from 1748. Sneak-thief, one who enters through unsecured doors and windows to steal, is recorded by 1859; the movies sneak-preview of a film before official release is from 1938.

"a sneaking person; person of selfish and cowardly temper and conduct," 1640s, from sneak (v.). By 1700 as "act or practice of sneaking."

Middle English awei, from late Old English aweg, earlier on weg "on from this (that) place;" see a- (1) + way (n.).

The meaning "from one's own or accustomed place" is from c. 1300; that of "from one state or condition to another" is from mid-14c.; that of "from one's possession (give away, throw away) is from c. 1400. Colloquial use for "without delay" (fire away, also right away) is from the earlier sense of "onward in time" (16c.). The meaning "at such a distance" (a mile away) is by 1712. Intensive use (as in away back) is American English, attested by 1818. Of sporting events played at the other team's field or court, by 1893.

also lay-away, 1961 in reference to a system of payments for reserved merchandise, from the verbal phrase (attested from c. 1400 as "to put away," especially "place in store for future use"); see lay (v.) + away (adv.). Earlier in the same sense, as an adjective, was Australian lay-by (1930).

also getaway, 1852, "an escape," originally in fox hunting, from verbal phrase get away "escape" (early 14c.); see get (v.) + away (adv.). Of prisoners or criminals from 1893.

as a game, 1925, from verbal phrase (attested from late 14c.); see keep (v.) + away (adv.).

also giveaway, "act of giving away," 1872, from verbal phrase give away, c. 1400 (of brides from 1719); see give (v.) + away (adv.). The phrase in the meaning "to betray, expose, reveal" is from 1878, originally U.S. slang. Hence also Related: give-away (n.) "inadvertent betrayal or revelation" (1882).

also faraway, "distant, remote," 1816, from far + away.

of coats, "cut back from the waist," 1841, from the verbal phrase; see cut (v.) + away. As a noun, "coat cut back from the waist," by 1849. In reference to models, drawings, etc., of which a part is cut away to reveal the interior, by 1946. The verbal phrase is from c. 1300 as "cut (something) off or away." 

c. 1300, lurken "to hide, lie hidden," probably from Scandinavian (compare dialectal Norwegian lurka "to sneak away," dialectal Swedish lurka "to be slow in one's work"), perhaps ultimately related to Middle English luren "to frown, lurk" (see lower (v.2)). From late 14c. as "move about secretly;" also "escape observation." Related: Lurked; lurking.