1550s (implied in sneakish), perhaps from some dialectal survival of Middle English sniken "to creep, crawl" (c. 1200), related to Old English snican "to sneak along, creep, crawl," from Proto-Germanic *sneikanan, which is related to the root of snake (n.). Of feelings, suspicions, etc., from 1748. Transitive sense, "to partake of surreptitiously" is from 1883. Related: Sneaking. Sneak-thief is recorded by 1859; sneak-preview is from 1938.
1590s, "one who sneaks," agent noun from sneak (v.). Meaning "rubber-soled shoe" is attested from 1895, American English; earlier sneak (1862), so called because the shoe was noiseless. See also plimsoll; another early name for them was tackies (1902), from tacky (adj.1).
The night-officer is generally accustomed to wear a species of India-rubber shoes or goloshes on her feet. These are termed 'sneaks' by the women [of Brixton Prison]. ["Female Life in Prison," 1862]
by 1942, noun ("a cowardly escape, an evasion") and verb ("sneak off, escape, give up without trying"), American English slang, perhaps from cop a plea (c. 1925) "plead guilty to lesser charges," which is probably from northern British slang cop "to catch" (a scolding, etc.); as in cop a feel "grope someone" (1930s); see cop (v.). Sense of "evade an issue or problem" is from 1960s.