- sly (adj.)
- c.1200, from Old Norse sloegr "cunning, crafty, sly," from Proto-Germanic *slogis (cf. Low German slu "cunning, sly"), probably from base *slog- "hit" (see slay), with an original notion of "able to hit." Cf. German verschlagen "cunning, crafty, sly," schlagfertig "quick-witted," literally "ready to strike," from schlagen "to strike." A non-pejorative use of the word lingered in northern English dialect until 20c. On the sly "in secret" is recorded from 1812. Sly-boots "a seeming Silly, but subtil Fellow" is in the 1700 "Dictionary of the Canting Crew."