Look in the OED & you'll find "brrrr", with a rare 4 Rs: it's this one of the traditional 8 parts of speech
[DOC] [TLE] WEEDS IN THE GARDEN OF WORDS - the political avenue [PAR] ever, such tidy classifications are never the reality and you'll find there is some ..... 
verb and turning it into a different part of speech for a bit more colour.