ᴱ√HESE¹ root. “brother or sister”
The root ᴱ√HESE appeared in the Qenya Lexicon of the 1910s with various derivatives having to do with siblings and blood relationships (QL/40). In the contemporaneous Gnomish Lexicon the root was given as heth¹ (GL/48), but it is not clear whether this was a replacement or a variant root for ᴱ√HESE.
Neo-Eldarin: I would adapt this as a Neo-Root ᴺ√KHETH “sibling, consanguinity” to serve as the basis for gender-neutral “sibling” words.
References ✧ GL/48; QL/40