There are two explicit explanations of Ecthelion's name given by Tolkien in material reproduced within the volumes of The History of Middle-earth. Both derive the name from the Elvish ecthel, but in one case (in volume II) that word is interpreted 'fountain', whereas in the other (in volume V) it is defined as 'spear-point', with a quite different etymology.

It seems certain that 'fountain' was the earlier interpretation, and given that Ecthelion is consistently referred to as 'Ecthelion of the Fountain', it hardly seems plausible that the original definition simply slipped Tolkien's mind. Rather, at least as far as the limited evidence suggests, it does appear that the later 'spear-point' interpretation was a deliberate change, or at least intended as a secondary meaning that happened to coincide with the first.