according to the american heritage dictionary of the english language, fourth edition...it's also a nickname for michael.
"CONTENTS hahaha183; INDEX hahaha183; ILLUSTRATIONS hahaha183; BIBLIOGRAPHIC RECORD
The American Heritagehahaha174; Dictionary of the English Language: Fourth Edition. 2000.
mick
PRONUNCIATION: mk
NOUN: Offensive Slang Used as a disparaging term for a person of Irish birth or descent.
ETYMOLOGY: Probably from the name Mick, nickname for Michael."
i can't post links yet, but if you google, "mick, nickname for" it's the first link.