A Sindarin word for “fourth” appearing in notes on numbers associated with The Rivers and Beacon-hills of Gondor from the late 1960s, an adjective form of canad “four” using the suffix -ui (VT42/25). In author’s note 5 of that document, Tolkien said that canthui was from the Southern dialect of Sindarin, saying that medial nasal-stop combinations like nt survived North Sindarin and implying the word was cantui in that dialect (VT42/27). He further said that in Southern Sindarin, nasal-stops combinations became nasal-spirants [nt > nth] and then later became long voiceless nasals [nth > nh]. Finally, he indicated that the older spelling nth was retained, and was sometimes restored in pronunciation by scholars.

Earlier drafts of The Rivers and Beacon-hills of Gondor had cantui and canhui “fourth” (VT42/10), perhaps representing the North/South Sindarin pronunciations (or archaic vs. modern).

Neo-Sindarin: For purposes of Neo-Sindarin, I use the form canthui “fourth” to represent this word as it is spelled. In terms of pronunciation, any of canthui, canhui, or cannui are possible, but I favor the scholarly pronunciation canthui for simplicity.