Definition of Root for

Babylon English Dictionary
(Slang) encourage, applaud a contestant, cheer
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Root for Definition from Language, Idioms & Slang Dictionaries & Glossaries
ENGLISH IDIOMS 2.EDITION
cheer for, pull for Who are you rooting for - the Leafs or les Canadiens?
English Idioms WM 1.3a
cheer for, pull for 
Who are you rooting for - the Leafs or les Canadiens?
Australian Slang
give encouragement to, or applaud, a contestant, etc. [originally US slang (late-19th C.)]