Lalaith claims: 'Rohirric has never been used by Tolkien. It seems that Foster has invented it for the occasion of writing his guide, perhaps modelling it on Adûnaic.' It seems to be the preferred term in current use, though, e.g. Ardalambion uses it without comment; I just thought I should mention that. Rohanese and Rohirian are suggested as alternatives; Lalaith actually uses Rohirin, just to add to the confusion.
Rohirric was related to Westron (the Common Speech), but with a more archaic feel to it. Tolkien translated it using actual Old English (holbytla, théoden, eorl etc.) to indicate this relatedness.
Dwarvish was if anything Semitic in inspiration: the alternation between Khazâd "Dwarves", Khuzdul "Dwarvish", and a possible construct state in Khazad-dûm "Moria" looks a lot like Semitic triconsonantal roots.