: Some of these, or related folk, are recorded as settling in
: Gondor and eventually becoming assimilated, their mounted
: prowess would undoubtably have been made use of by the
: Gondorians...

The Northmen who settled in Gondor predated the Eotheod by centuries. The Eotheod were descended from the surviving cavalry of the army of the Kingdom of Rhovanion. Tolkien doesn't say the army included infantry, but he seems to imply that the bulk of the army (which was destroyed by the Wainriders) was not mounted.

:...Earnur was certainly mounted when he was cowed by
: The Witch King, this is suggestive that the upper classes, if
: not others as well, of Gondor had some skill in mounted combat,
: though they were not from a purely horse-based society like
: Rohan...

It suggests that the officers of the army, not necessarily derived solely from the upper classes, would have been mounted.

:... The Rangers of the North were mounted, and the fact
: that they took the trouble to bring Aragorn's own horse from
: the far north suggests that the steeds they rode were trained
: war-horses (if they were merely riding horses then why go to
: the trouble of bringing a specific one all that way?). This
: suggests that mounted combat was an accomplishment of Dunadan
: nobility in general.

There is no way to connect the Rangers' use of horses with any traditions in Gondor. The Rangers had to cover a lot of territory. Gondor had a standing army to maintain its borders and keep bad things outside from getting in. Whether it also relied upon local forces in that operation doesn't reflect on the fact that the Rangers had to be a different kind of force from what Gondor had. Faramir's rangers in Ithilien, serving in a similar capacity but over a much smaller area, were not mounted.

:...Also, as a general point, if the Gondorians realised that a
: mounted element in an army was desirable (as is shown by their
: recruitment of the Eothed) then one imagines that they would
: make some efforts to raise at least a modest native cavalry
: contingent.

It's debatable whether Gondor would have sent its own cavalry north, given that Earnil was so unsure of his ability to send any aid at all for many years. He sent an expeditionary force, not the greater part of Gondor's army. The Eotheod may have proved more useful working alone than incorporated into Gondor's native cavalry.

: : I think 300 is too high for the knights, and the men-at-arms
: : are never said to ride into battle.

: The bulk of the cavalry led by Imrahil at the battle are not
: described, they could have included his men-at-arms, and
: possibly some of the Tower Guard (who as elite troops probably
: had mounted capability).

Or just a cavalry company or two stationed in Minas Tirith. There is no reason to give a high probability to Imrahil's leading a thousand horsemen to battle. Such a force should have been able to accomplish more than they did against the vanguard of the Witch-king's army.
: : Tut, tut! Tolkien was a linguistic scholar. He never called
: : himself a medieval scholar. Someone recently contacted Tom
: : Shippey and asked him what he thought of the idea of Tolkien
: : as a medieval scholar. Shippey's answer (I'm summarizing) was
: : that, if pressed, Tolkien might have conceded to being a
: : medievalist, but not in the sense most people use the word
: : today. But Shippey was quick to point out that Tolkien
: : thought of himself as a philologist, and often said so.

: He was a scholar specialising in a language which was first
: written down in around 650 AD and ceased to exist as such by
: around 1200 AD. I think he was perforce well versed in the
: Mediaeval era.

He also studied Greek, Latin, Hebrew, Gothic, and other languages. Tolkien did not confine himself to Anglo-Saxon.

: : That is really a small nit, but I don't think it's necessary
: : to imply that Tolkien was a medievalist for this point,
: : Martin. I don't know the etymology of "man-at-arms", but
: : Tolkien's philological background would have acquainted him
: : with it.

: I think it is well acknowledged that Tolkien was careful in the
: language that he put down on paper. By the time English began
: to be used in written form again the Latin term miles (meaning
: a fully equipped heavy cavalry man) and the French term gen
: d'armes were translated as man-at-arms. I don't think Tolkien
: would have been unaware of this meaning. It is at least
: possible that Tolkien was using the term in this sense.
: Nothing in the text is directly contrary to this at least. A
: man might be perceived as tall even when mounted, particularly
: if his feet trailed on the ground like Hrolf Ganger (Rollo) the
: founder of Normandy!

I'm not saying he would have been unaware of the meaning. In fact, dictionary.com gives essentially the same meaning as you, so it's supposed to still mean the same thing (although modern fantasy authors seem to be trying to change that). But the only possible indication of numbers of horsemen Tolkien gives for Minas Tirith is in "The Last Debate" where he writes that "another company of five hundred hundred horse there should be, among which would ride the sons of Elrond with the Dunedain and the knights of Dol Amroth".

If Imrahil was the only guy in town to have horses, I'd say this was a strong argument in favor of your interpretation (in addition to the traditional meaning of the term "man-at-arms"). But Denethor had SOME horsemen of his own. This is established at least indirectly through references to the stables by the beacon towers in UNFINISHED TALES.

But Tolkien used old words in new ways. He delighted in giving them new but familiar meaning. Who is to say he did not do this with "men-at-arms"?

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