S: (v) slip, sneak (pass on stealthily) "He slipped me the key when nobody was looking"
Adjective
S: (adj) furtive, sneak, sneaky, stealthy, surreptitious (marked by quiet and caution and secrecy; taking pains to avoid being observed) "a furtive manner"; "a sneak attack"; "stealthy footsteps"; "a surreptitious glance at his watch"