Early Quenya
rendo
noun. kinsman, cousin
réro
noun. kinsman, cousin
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 noun appearing as ᴱQ. {rendo >>} rēro (rendo) “kinsman, cousin” in the Qenya Lexicon of the 1910s, under the early root ᴱ√RESE “aid, support ?” (QL/79); the question mark was Tolkien’s. Tolkien later added a note to this entry clarifying that the “kin, cousin” words were derived from primitive reðe; see the entry on ᴱ√REÐE for further discussion.
Neo-Quenya: I would adapt this word as ᴺQ. rendo “male cousin, kinsman or relative” from a Neo-Root ᴺ√RE(N)D.