Archaic Qenya cognate of G. Gwarestrin “Tower of Guard” in an early name list (PE13/102), perhaps a combination of some form of the verb tiri- “to guard” and tirion “tower”.
Early Quenya
tiri-
verb. to watch; to keep, guard, preserve; to look at, gaze at, observe
tirin
place name. Tower
tirion
noun. (great or mighty) tower; city on a hill
tiri(o)stirion
place name. Tiri(o)stirion
Name of Ingil’s tower in the earliest Lost Tales (LT2/5), it is simply tirin “tower” used as a name (LT1A/Kortirion).