Although slyboots has the meaning of “a crafty or cunning person,” it is closely related to footpad, “a thief”; gumshoe, “a detective”; pussyfoot, “a prying, nosy person”; also to the German Leisetreter (light treader), “a sneak, spy”; and the French pied plat (flat foot), “a sneak, knave.”
All of these carry the common connotation of a person who moves with quiet or stealth, and always these movements are contrary to the well-being or comfort of the one applying the term (even the gumshoe is so-called only by the one who is attempting some clandestine act).
The American flatfoot, of course, is quite different from the French, being a policeman, specifically, one who has walked on patrol for so long that his arches are presumed to have fallen and, in fact, he has acquired flat feet.
