s-stems in Slavic and Germanic

I was wondering if such s-stem words could be derived from PIE, or be just innovations or s-extensions. There's a bunch of matches that seem to be IE-widespread, like *nebHos (Greek nephos=Hit napash=Skt nabhas=Slav nebo) and *g^en(h?)os (genos=genus=janas). Greek has a long listmof words including abstract nouns (takhos, me:kos, brakhos), animal names (ke:tos "sea monster", te:thos "oyster", selakhos "shark", temakhos "fish sliced"), natural phenomena (skotos, khaos, nephos).
The examples of genos and menos were the simplest constructions: nouns derived from verbal roots with s-suffix (gen(h)-os, men-os), but in another examples the suffixation seems to be more hard to explain. Temakhos seems obviously derived from *temh-" to cut, but with an ending that not seems regular in Greek (kh<h?)

Latin is also full of such names (genus, munus, foedus, scelus, etc), but I don't know about Celtic examples, probably they existed too.
JS Lopes