Early Quenya
tuksainen
cardinal. thousand
tuksa kainen
cardinal. thousand
maite
cardinal. thousand
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 variant word for “thousand” from the Early Qenya Grammar (EQG) of the 1920s as a combination of ᴱQ. tuksa “hundred” and ᴱQ. kainen “ten”, following the pattern of words like ᴱQ. kan(ta)kainen “forty” (PE14/50, 83). Properly it is tuksa kainen, shortened to either tuksakainen or tuksainen. Compare ᴱQ. húme “thousand”.