Gnomish
cas
noun. head, skull
corob
noun. skull
nôl
noun. head
ontha
pronoun. his
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A word appearing as G. corob “a skull” in the Gnomish Lexicon of the 1910s (GL/26), likely related to ᴱ√KORO “be round” (QL/48).
Neo-Sindarin: Since √KOR “round” survived in Tolkien’s later conception of the languages, I’d retain this word as ᴺS. corob “skull”, especially since other early “skull” words such as ᴱN. cas derived from ᴱ√KASA “head” were probably no longer viable since non-initial s generally vanished in Sindarin.