Early Quenya
tiri-
verb. to watch; to keep, guard, preserve; to look at, gaze at, observe
tirion
noun. (great or mighty) tower; city on a hill
tiri(o)stirion Archaic
place name. Tiri(o)stirion
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.
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”.