I m so tired about the JRRT and mail discussion... fact actually IS he DOES not use any other word for armor in his published stories, but if you look beyond that, in his poems and wordlists... he DOES use the terms breastplate, cuirass, corslet, panoply... even harness. AND now don' t tell me he did not know what these terms meant, the guy was a linguist.
Yes he uses mostly mail, often byrnie, byrne, hauberk, haubergeon... yet it is a modern practice to restrict most of these terms to chain, it wasn't even used "the technical right " way in many contemporary medieval sources, and now don't tell me the guy didn't know... he was a medievist after all ☺
And often even if he used "mail" , when we look at the actual description he seems to describe possibly scale, splint or lamellar armour... best example "fishmail", obviously NOT chain! I wouldn't even rule out segmented or ring armour sometimes, nor would i coat of plates or half-plate...
However i absolutely WOULD think about in which time and era it is used and mentioned...
There almost certainly is NO real metal armour, except for the valar, before the dwarves come out with chain...
the Noldor do not use chain at first, they use "fishmail",
At later times them we have Thingol weaing both , "fishmail" plus a "corslet", which i interpret almost certainly as neither chain nor scale but at least as some sort of brigandine, if not really a cuirass or plate in sense of breastplate.
Second age and third age needs to be excamined separately...