[The Squatter of Amon Rûdh]

Well, a quick glance at the OED confirms that OE mōt is the source of the modern English noun 'moot', and by association the adjectival form (e.g. 'moot point'). Gemot is just that word with the prefix ge-, which indicates that this is the verb form and that it implies 'met', i.e. 'The wise met [in conclave]'.

I think that entmoot was suggested as soon as Tolkien decided to name his new race after the giants of Old English literature. Since ent and mōt are both Old English, it seems logical to make them into the sort of compound that occurs in Old English. The spelling is modernised to 'moot' simply because he was aiming at a general audience. This term also avoids further recourse to 'council' (OF cuncile from lat. concilium: 'assembly', although this is a pre-Conquest loan-word). Before we read too much into any of this, though, there's no evidence that Thingol's name really has anything to do with gatherings or assemblies, and the terms Tolkien decides to use in the Third Age are entirely logical given the context.

Everywhere I look, ent is translated 'giant', but there seems to have been something special about Ents. Beowulf kills Grendels mother with a sword that is the work of ents; the city in The Ruin is their handiwork too, as are the Roman towns referred to in Maxims II. Aside from that, though, Goliath is se ent goliað, and the word is used to gloss Latin gigas: 'a giant'.