§ Fen Fornen, Fenn Forn ’the Closed Door’, Fenn uiforn ’the Ever Closed’ (WR:338,341)
§ Uidavnen, davnan (WR:341)
These are earlier names of Fen Hollen ’Closed Door’, see the description:
Turning westward they came at length to a door in the rearward wall of the sixth circle. Fen Hollen it was called, for it was kept ever shut save at times of funeral, and only the Lord of the City might use that way, or those who bore the token of the tombs and tended the houses of the dead. (LotRV, ch.4; RC:550)
The Etymologies give N. fend, fenn ’threshold’ (PHEN-), but forn is the adjective ’right or north’ (PHOR-), not ’closed’. So it seems that Tolkien planned a revision of roots or created a new one (homophonous PHOR-, *SPOR-?) with the meaning ’close’. The form uiforn is then formed with the prefix ui- from OY- ’ever, eternal’.
The adjectives #tavnen < uidavnen *’ever-closed’ and #tavnan seem to be derived from TAP- ’stop’, whence Q. tape ’he stops, blocks’ (VT46:17), tampa ’stopper’. One can thus suspect *tapninā > *taphnena > tavnen or *tapnanā > *taphnana > tavnan. Compare lepn- > levnui (VT42:26)