Now follow earlier names of the rivers of Gondor. Their final forms, which were ultimately published, are explained in VT42:7-18. As it can be seen from these late explanations, the linguistic situation in that area was very complicated and not all names of the rivers are even Sindarin. Most of them already occur in these early writings:
§ Ithilduin, Duin Morghul (TI:312)
The former name clearly means *’moon-river’, consisting out of N. Ithil ’poetic name of the Moon’ (THIL-) and duin ’river’ (DUI-, VT45:11).
The latter must mean *’river of dark magic’, the second word consisting out of the element mor- ’black’, appearing in many other names (see MOR-) and lenited gûl ’magic’ (ÑGOL-).