Knights

Dating the use of this term is difficult, especially as its meaning seems to have changed over time. We know that Thingol had 'knights' in his service among the armies of Doriath, so at least some warriors who could be given the title existed during the First Age, though these seem to have been distinct from the mounted knights of the Dúnedain in later ages. While we have no direct references to knights during the Second Age, their presence among Isildur's followers at the beginning of the Third Age strongly implies that there were Númenórean knights during the preceding age. In the closing years of the Third Age, the Swan-knights of Dol Amroth fought in the Battle of the Pelennor, so the tradition clearly lasted through the Third Age in some form, and apparently on into the Fourth Age.

The Elvish word roquen literally meant any horse-rider, but among the Dúnedain it came to be used as a superior military rank. In English, the word 'knight' also evolved over time; it originated with Old English cniht, an attendant or servant, though over the centuries it came to be used especially for mounted soldiers. In this more common later usage of an armoured horseman, it matches well with the rank of roquen among the armies of the Dúnedain.

That is, our only specific account of the rank of roquen among Men, but there is an account from the First Age of Thingol giving Túrin '...a place among the knights of my sword...' (Unfinished Tales Part One II, Narn i Hîn Húrin). This does not seem to be equivalent to the later usage of 'knight' (there's no suggestion that Túrin was a mounted soldier) and is probably intended simply as a convenient term for a royally appointed warrior.