"rather sneaking, mean and stealthy," 1833, from sneak (v.) + -y (2). Sneakish is from 1864. Related: Sneakily; sneakiness. Sneaky Pete "cheap liquor" is from 1949.
Entries linking to sneaky
sneak v.
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.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.