from http://www.macquariedictionary.com.au/

grot
noun 1. filth: Wipe that grot off. 2. a filthy person. [backformation from grotty]


grotty
adjective 1. dirty; filthy. 2. of poor quality; nasty. [originally British slang (1960s); alteration of grotesque + -y; apparently originally Liverpool slang, and first widely popularised by The Beatles; the earliest record of this word is from the Beatles movie A Hard Day's Night which was released in 1964