sneaky vs underhanded

sneaky and underhanded both are adjectives.

Word	Noun	Adjective	Verb	Adverb
sneaky	No	Yes	No	No
underhanded	No	Yes	No	No

As adjectives, sneaky and underhanded are synonyms defined as:

Other synonyms of sneaky include underhand.

sneaky (adjective)	underhanded (adjective)
marked by quiet and caution and secrecy; taking pains to avoid being observed	with hand brought forward and up from below shoulder level
marked by deception	marked by deception