sur ‧ rep ‧ ti ‧ tious /ˌsʌrəpˈtɪʃəs◂ $ ˌsɜː-/ BrE AmE adjective
done secretly or quickly because you do not want other people to notice:
Rory tried to sneak a surreptitious glance at Adam’s wristwatch.
—surreptitiously adverb
—surreptitiousness noun [uncountable]