Such a bunch of bold and often self-consciously multi-syllabic synonyms for “furtive”, a word entirely devoted to going unnoticed. The time and racket required to put some of these synonyms to voice would put all but the most stealthy spies at risk of discovery, or elimination.
And then there’s Sly. An incision. A silencer. A whisper out of the darkness. A three-letter utterance without even an anchoring vowel. The word itself is a hiss, a diversion for the covert “y”.