Gnomish
ress
noun. cousin (f.), relative
goredhnir
noun. cousin (f.)
goredhwin
noun. cousin (f.)
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.
G. ress appeared in the Gnomish Lexicon of the 1910s as a word for a female cousin or relative based on the early root ᴱ√redh- (GL/65). It had poetic equivalents G. redhwin and redhir, which also appeared in the more elaborate forms G. goredhwin or goredhnir (GL/41). Two more variants, G. hethres and G. gedres (with deleted variant {gedhris}), referred to first and second female cousins respectively, with the prefixes G. heth (for close relation) and G. ged (a more distant relation) respectively (GL/38; GL/48).
Neo-Sindarin: I would retain ᴺS. ress as a Neo-Sindarin word for “female cousin or relative” as a derivative of the Neo-Root ᴺ√RE(N)D, but would abandon all the more elaborate variants. This form cannot be a direct result of ancient ✱red+se, so I think the ss is the result of analogy from other feminine forms like S. bess “wife”.