- on the sly
|part of speech:
||slier, slyer, sliest, slyest
||devious or not to be trusted.
The guard had to be extra careful with the sly criminal.
- crafty, cunning, tricky
- similar words:
||crafty in a funny way; full of mischief.
Her sly smile told me it was all a joke.
||on the sly
||slyly (adv.), slyness (n.)