Italian Etymology Literally, “on the wire of the razor”. Compare French sur le fil du rasoir. Prepositional phrase sul filo del rasoio (idiomatic) on the knife-edge, on the edge, on thin ice camminare sul filo del rasoio ― to walk a tightrope (literally, “to walk on the knife-edge”)Wikiwand - on Seamless Wikipedia browsing. On steroids.