Early Primitive Elvish
reðe
root. kinsman
rese
root. kinsman
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.
The form reðe was a root added under ᴱ√RESE [REÞE] “aid, support” in the Qenya Lexicon of the 1910s, with derivatives of ᴱ√RESE having to do with “kinship” reassigned to reðe, such as ᴱQ. renda “related, of the same kin or clan” and ᴱQ. resse “kinswoman, cousin” (QL/79). In the contemporaneous Gnomish Lexicon Tolkien had a similar set of words likewise derived from distinct reth- vs. redh-, with the latter most likely being the basis for words like G. redhin “related” and G. ress “cousin (f.), relative” (GL/65). The root was given as RESE- “kinsman” in the Poetic and Mythological Words of Eldarissa (PME/79), but the addition of reðe may be later than that document.
Neo-Eldarin: For purposes of Neo-Eldarin, I think it is worth positing a Neo-Root ᴺ√RE(N)D to preserve these early kinship and cousin words, for which we have no later alternatives. It might be considered a variant of later root √RED “scatter, sow” (Ety/RED; PE19/91) and thus applied only to more distant kin.