slang One who is apt to drink alcohol often and excessively; an alcoholic. "Grog" refers to rum that has been diluted with water. It was named after Edward Vernon, an 18th-century British admiral nicknamed "Old Grog" (because he wore a grogram cloak) who ordered that his sailors receive that mixture instead of pure rum. Geez, if we go to the bar a third time this week, we're gonna look like a couple of groghounds!