An adjective glossed “mortal, dying” with variant forms firin or firen appearing as an element in alfirin “immortal” (PE17/101).
Conceptual Development: The adjective [N.] firen had the gloss “human” in The Etymologies of the 1930s under the root ᴹ√PHIR (Ety/PHIR).
Neo-Sindarin: For purposes of Neo-Sindarin I would use this adjective largely for “one in the process dying”, and for “mortal (= one capable of dying)” I would use fíreb.
>> firin