Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!

Qenya 

alfírimo

noun. Immortal

alfírima

adjective. immortal

An adjective for “immortal” in the Quenya Verbal System (QVS) from 1948 appearing only in its plural form alphírimar, using the adjective plural formation of QVS (PE22/124). Its more typical Quenya adjective plural form would be alfírime. It also appeared in a noun plural form Alphírimor “Immortals”. It is a combination of ᴹQ. fírima “mortal” with the negative prefix ᴹQ. al-.

Conceptual Development: In The Etymologies of the 1930s the word for “immortal” was ᴹQ. ilfirin, a combination of ᴹQ. il- “not” and firin “dead (by natural cause)” (Ety/PHIR).

ilfirin

adjective. immortal