"stealthy" in the adjective sense
1. 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"
Source: WordNet® (An amazing lexical database of English)
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