⋄ Orendil >> Elendil (RS:197-198,260,270)
⋄ Ithildor >> Isildor >> Isildur (RS:261,271,320)
Tolkien hesitated about the names of Sauron’s defeaters and he also considered Valandil (cf. VT46:4, LR:60) for later Elendil.
The first name, Orendil, could mean *’lover of the sunrise/morning’ with #ore as Q. óre ’rising’, anaróre ’sunrise’ (ORO-), Early Qenya ōre ’the dawn, Sun-rise, East’ (QL:70) and the suffix -(n)dil which implies ’devotion’, ’disinterested love’ (Silm.index) and is usually translated as ’lover’, e.g. Aiwendil ’Lover of Birds’ (UT:401, NIL-, NDIL-). Compare also the name Orendel from a Middle High German poem probably having connotations with sunrise and morning, being a cognate of Old English Ēarendel, which was Tolkien’s inspiration for his character Earendel, later Eärendil (Let:297).
Ithildor contains N. Ithil ’poetic name of the Moon’ (THIL-) and the suffix taur < taurā ’mighty’ often found in names, as Tor-, -dor (TĀ-,TAƷ-). However, in Isildor Q. Isil ’moon’ is substituted, but Quenya usually does not change ā > au > o as Noldorin/Sindarin. So perhaps Isildor should be interpreted as containing the suffix -do as in pl. Hildor ’the Followers’ < KHILI (WR:387) or Q. meldo ’friend’ (VT45:34) < MEL-; and another name-formative or agentive suffix -r.