The usual word for “horse” in Quenya, a derivative of ✶rokkō (Let/282, 382; WJ/407) and very well attested. There are indications that this word was more specifically a “swift horse” (Let/382; EtyAC/ROK), but in most cases Tolkien used it generically.
Conceptual Development: ᴹQ. rokko “horse” first appeared in The Etymologies of the 1930s under the root ᴹ√ROK “run on foot”, already with the derivation given above (Ety/ROK). The relevant entry appeared twice; in one rokko was first written as rokka “wheel”, and in the other the form was first written ronko, but in both cases Tolkien revised the word to rokko “horse”.
rocco ("k")noun "horse" (ROK, SA:roch; Letters:382; cf. 282 where the spelling really is rocco, not rokko_). _In Letters:382 the word is defined as "swift horse for riding". VT46:12 refers to an alternative form of the entry ROK that was inserted into the Etymologies; here rocco, which Tolkien revised from ronco ("k"), was similarly glossed "swift horse". Nésë nórima rocco ("k") "he was a horse strong/swift at running" (VT49:29)