A word appearing as G. arn “son” in the Gnomish Lexicon of the 1910s (GL/20), also appearing with the same form and meaning in Gnomish Lexicon Slips modifying that document, but with a new plural form eirn (PE13/110). The word reappeared in Early Noldorin Word-lists of the 1920s but there its gloss was changed from “son” to “child” (PE13/137). In the Early Noldorin Dictionary of the 1920s its only gloss was “child” (PE13/160). There is no sign of this word thereafter.
Early Noldorin
gir
noun. interior, inwards, centre, inner parts, inside, heart
girdh
noun. entrails, bowels, inwards
arn
noun. child, child, [G.] son
barch
noun. horror
A word appearing as ᴱN. girdh in Early Noldorin Word Lists of the 1920s, glossed either “inwards, entrails” (PE13/144) or “entrails, bowels” (PE13/161), with “inwards” being an archaic English variant of “innards” according to the editors. This word was originally a plural form of ᴱN. gir “interior”, from primitive ᴱ✶ʒirdǝ.
Neo-Sindarin: I would adapt this word as ᴺS. irdh “entrails, bowels” for purposes of Neo-Sindarin based on this primitive form, since the ʒ vanished in Sindarin.