sneak

a person who is regarded as underhanded and furtive and contemptible

someone who prowls or sneaks about; usually with unlawful intentions

someone acting as an informer or decoy for the police

to go stealthily or furtively; "..stead of sneaking around spying on the neighbor's house"

put, bring, or take in a secretive or furtive manner; "sneak a look"; "sneak a cigarette"

make off with belongings of others

pass on stealthily; "He slipped me the key when nobody was looking"

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"