sly /slaɪ/adjective 4adverb 1forms 4phrases 1 adjective4 •Artfully cunning; secretly mischievous; wily. •Dexterous in performing an action, so as to escape notice •Done with, and marked by, artful and dexterous secrecy; subtle •Light or delicate; slight; thin. adverb1 •Slyly. formsslier · slyer · sliest · slyest Phrases with sly on the slySlyly, in an inconspicuous manner, so as not to be seen; secretly; stealthily.