Do we have an (in-universe) etymology for this word? The {SoS} element
suggests that it might have once meant "womb" or something similar, and
then drifted to the meaning of "core".
Very few words are given in-universe etymologies. Also, most multi-syllable root words will have single-syllable words contained in them, so I don't think it's necessarily significant in-universe that {SoSbor} is made of the words for "mother" and "gurgle".