Английский Этимологический словарь - stumble (v.)

- c.1303, possibly influenced by stumpen "to stumble," but probably from a Scand. source (cf. dialectal Norw. stumla, Swed. stambla "to stumble"), probably from a variant of the P.Gmc. base *stam-, source of O.E. stamerian "to stammer." Stumbling-block first recorded 1526. Stumblebum "alcoholic derelict" first recorded 1932.