Synonyms and related words :
artfully, astutely, cagily, cannily, cleverly, cunningly, deceitfully, foxily, fraudulently, furtively, indirectly, insidiously, knowingly, on the sly, shiftily, shrewdly, slick, slyly, smoothly, subtilely, subtlely, surreptitiously, treacherously, trickily, underhandedly, warily, wilily