• (adv.) Notoriously, in an ill sense; infamously; impudently; shamefully.
Ar'rant·ly adverb Notoriously, in an ill sense; infamously; impudently; shamefully. L'Estrange. 
arrant, arrantly 1. Used to emphasize that someone or something is an extreme example of something disapproved of. 2. Without qualification; used informally as (often pejorative) intensifiers; such as, an arrant (complete) fool; He dismissed the rumors as 'arrant nonsense'.