*stūpaną

Related to *staupaz (‘steep’) and *staupijaną (‘to pour’), thus seeming to reflect a pre-Germanic root *stewb-. However, the rarity of *b in Proto-Indo-European and cognates such as Latin stupeō (‘to be stunned’) make it more likely that the root was *stewp- (‘to push, hit, knock’) with a semantic shift to “fall (over)”, and so Germanic *steup-, *stūp- could have been back-formed from earlier *stupp-, from pre-Germanic *stup-né(h₂)-; this process has been used to explain many other instances of root-final *p in Germanic. Compare also Proto-Germanic *stubbô, *stubbaz (‘stump, stub’).

Kroonen derives the Germanic from a homophonous root *stewp- (‘to stoop, bend’), implicitly considering it etymologically separate from the "push, hit" sense above, and adduces only Welsh ystum (‘a bend, turn’), Breton stumm (‘idem’) as cognates.