: : Ettin (etten) has a similar Anglo-Saxon origin to Ent. But I think here Tolkien was using the word in it's original meaning: ie a man-like creature of giant size. So in this particular case I would imagine the "Ettins" in question were trolls.

: ::: I agree with the notion that trolls were the basis for the word "Ettenmoors". Remember that Fangorn, boasting of his strength, said that Morgoth had created the trolls in mockery of the Ents, but the Ents were still many times stronger. And also remember the troll incident during the quest for Erebor in the Hobbit? I imagine that trolls had always lived there, but were for a time driven out during the power of Arnor, and then returned after Arnor ceased to exist.

I believe a further indication of the existence of a non-troll gargantuan life form in ME is the word found in the Etymologies 'Noroth' which means, you guessed it, giant, quite different from the term torog for troll.