Longman Dictionary of Contemporary English - snitch

~1 v informal 1 I + on to tell someone such as a parent or teacher about something that another person has done wrong because you want to cause trouble for that person 2 to quickly steal something unimportant or of little value ~2 n 1 informal someone who is disliked because he or she tells a parent or teacher about something wrong that another person has done 2 BrE humorous a nose