"sneaky" in the adjective sense
1. sneaky, underhand, underhanded
marked by deception
"achieved success in business only by underhand methods"
2. furtive, sneak, sneaky, stealthy, surreptitious
marked by quiet and caution and secrecy taking pains to avoid being observed
"a furtive manner"
"a sneak attack"
"a surreptitious glance at his watch"
Source: WordNet® (An amazing lexical database of English)
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