You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: ENGLISH USAGE 
Clue: Latin for "thus", this 3-letter word is put in brackets to indicate an error in a quote
sic

Category: A "COCK"-EYED CATEGORY 
Clue: A staged battle between 2 roosters
cockfight

Category: ORES 
Clue: The red, sometimes transparent crystals of cuprite are an ore of this metal

copper