A word for the seeing stones of Númenor, a combination of palan “far” and some form of the root TIR “see” (Let/427), hence: “far-seer” or “far-gazer” (LotR Index; PE17/25, 86). This word is unusual in that it has a long vowel in its final syllable, something that does not normally occur in Quenya words. The ancient form of this word was palantīrā̆ (Let/427), and the reduction of short vowels in long compounds was not unusual in Quenya, for example: Valinor as a shorter form of Valinórë. However, after such reductions long vowels in final syllables tended to shorten, so the expect form would be palantir, not palantír. In one place Tolkien described this word as a “a Numenorean formation” (PE17/86), perhaps as a way of explaining the unusual retention of a long vowel in its final syllable.
The usual rules for Quenya stress would put the stress on the second syllable: paLANtír. A common mispronunciation of this word put the stress on the final syllable: palanTÍR. The speech coaches for Peter Jackson’s Lord of the Rings movies instructed the actors to pronounce this word like English “lantern” to help them remember the correct stress pattern.
Conceptual Development: This word appeared in the Etymologies of the 1930s where it was probably a later addition. In its earliest appearances, both in Etymologies and the drafts of The Lord of the Rings, it was Palantir with a short i (Ety/PAL, TIR; WR/76).
palantír noun *"Far-seer", used = "Seeing Stone" (pl. palantíri is attested); see palan-. The form palantir (with a short i) appears in Letters:110.