A preposition meaning “through” in The Etymologies of the 1930s derived from ON. trī under the root ᴹ√TER(ES) “pierce” (Ety/TER), so presumably derived from ✱trē with ancient ē > ī as usual in Noldorin and Sindarin. In The Etymologies as published in The Lost Road Christopher Tolkien gave the Noldorin and Old Noldorin forms as trî and trí following the usual orthographic conventions of those languages (LR/392), but Carl Hostetter and Patrick Wynne indicated they were both trī in their Addenda and Corrigenda to the Etymologies (VT46/18).
Noldorin
benn
noun. man, male
dir avos-eithen miriel
dir avos-eithen miriel
dîr
noun. man, referring to an adult male (elf, mortal, or of any other speaking race)
dîr
noun. man, adult male; agental suffix
forodrim
noun. Northmen
forodwaith
noun. Northmen
forodwaith
noun. the lands of the North
forodweith
noun. Northmen
forodweith
noun. the lands of the North
godrebh
adverb. through together
tre-
prefix. through (but denoting completeness when prefixed to verbs, cf. English idioms like "talk something through")
tre-
prefix. through
tri
prefix. through (but denoting completeness when prefixed to verbs, cf. English idioms like "talk something through")
trî
preposition. through
trî
preposition. through
A prefixal form of N. trî “through” in The Etymologies of the 1930s, appearing as tre- when unstressed (the norm) and tri- when stressed, though there are no examples of the latter (Ety/TER). Presumably this refers to ancient rather than modern stress.