In Quenya the word for we is emmë and the corresponding pronominal ending -mmë, or elmë and the corresponding pronominal ending -lmmë, or the pronominal ending -lvë. Tolkien had different words for we depending if it included you (the person or persons spoken to) or not. Apparently in grammar this is called inclusive and exclusive we, something I learned. The last suffix may be for we when it means you (singular) and I. Tolkien also changed his mind about these pronouns for we. Pronouns are a less certain area in Quenya.
I didn't find a Sindarin word for we.