from Wiktionary, Creative Commons Attribution/Share-Alike License.
superlativeform of growly: most growly.
Sorry, no etymologies found.
Equipped with the growliest voice in movies, the burly McGraw became something of a star thanks to the sheer remorselessness he projects here, brutalizing confederates, cops and innocent bystanders alike with the same reflexive contempt for any life other than his own.
I said in the lowest, deepest, growliest voice I could muster.