Early Quenya
-(n)dóra
suffix. million
mindóra
cardinal. million
mindóre
cardinal. million
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 manuscript version of the Early Qenya Grammar (EQG) of the 1920s had ᴱQ. mindóra “[one] million” (PE14/50), but in the typescript version this became ᴱQ. mindóre “million” (PE14/83), a combination of ᴱQ. min “one” and the “-illion” suffix ᴱQ. -(n)dóre.
Neo-Quenya: I would retain ᴺQ. mindórë “million” for purposes of Neo-Quenya, as we have no better alternatives.