a question regarding Latin nasal

I wonder if this is an accident or not.
There are for instnace some words where the Latin has an nasal "n" at
the end of the word.
femina, serpens, catena (*catesna)
About the word "femina" I learn this is in fact originally an "fem" (I
hope this information is not wrong, is in my Stowasser dictionary). So
we have the form "fem-" as root
'serpens' seems to be a derivative from 'serpo'. Again here, the other
cognates in PIE languages shows no "n" but just *serp-
I take the word "catena"= handcuffs.
This Latin word comes from an older *catesna
These 3 words for instnace, have all 3 cognates in Rom. ( my opinion)
Latin. femina, rom. fem-eie - semantism OK
Latin serpens,- rom. Sarpe (dialectal Serpe) - semantism OK
Latin catena ( *catesna)= rom. catuSa -- semantism OK

1) Rom. Word "femeie" ( women) is givin as deriving from latin
"famiglia" (family)
2) rom. Word cãtuSa (handcuffs) is given with unknown etymology
3) the PIE cognates for "serpens" shows no "n".
4) there is the latin word "caterva"= Haufen, Scharr, Trup, Bande, some
people there, which derives from an older "*catesva".
5) the Rom. Word "cateva" or reg. "câteSva like cateStrei, cateSpatru ,
see DEX ) made me to see the connection catena ( *catesna) = catuSa



Question: can it be that Latin have had the habit of forming derivatives
with suffixes which have had this "n" there?

Alex