*euþą

(Kölligan 2024) provides two fresh possibilities for this derivation:

A full-grade nominalized verbal adjective: *h₁euH-tó-m (literally, ‘the suckled one’ or ‘the one given milk’) from Proto-Indo-European root *h₁euH- (‘to give milk, suckle’), with a formal analog in the word *kinþą (‘child’); or,

Applying a simple thematic nominal suffix *-o- directly to the extended Proto-Indo-European root *h₁éwHdʰr̥ / *h₁ówHdʰr̥ (‘udder’) yields *h₁éwH-dʰ-o-m (‘offspring of the breast/udder’).