From "An universal etymological English dictionary""An universal etymological English dictionary" By Nathan Bailey (1731):
a RAT [rat, F. ratta, Span. ratze, Teut. ratte, Du.] an amphibious kind of Animal, infecting Houses, Ships, &c.
[(obsolete) Teut. -> Teutonic -> Germanic]
From "A dictionary of the English language"A dictionary of the English language : in which the words are deduced from their originals, and illustrated in their different significations by examples from the best writers : to which are prefixed, a history of the language, and an English grammar"
By Samuel Johnson (1766):
RAT. f. [ratte, Dutch; rat, French; ratta, Spanish.] An animal of the mouse kind that infects houses and ships
This finding gives a hint that the origin of the word rat might be of Persian origin (and also Sanskrit) [ [WiktionaryWiktionary puts as "Middle Persian randītan (“to scrape, smooth”), Sanskrit rádati (“he gnaws, cuts”))."]
The Engligh rat takes its name from *red- 'gnaw, scrape' (cf. also Lat rōdō 'gnaw', MPers randītan 'scrape, smooth', Skt rádati 'bites, gnaws, cuts, makes way, opens').