[adj] lacking principles or scruples; "the rascally rabble"; "the tyranny of a scoundrelly aristocracy" - W.M. Thackaray; "the captain was set adrift by his roguish crew" [adj] playful in an appealingly bold way; "a roguish grin"
blackguardly, devilish, dishonest, dishonorable, playful, rascally, scoundrelly