(This definition is cited from Merriam-Webster's Collegiate Dictionary: http://www.m-w.com/cgi-bin/dictionary.)
an exaggeratedly styled man's suit of the 1940s, consisting of baggy pants with tight cuffs and an oversized coat with wide lapels and padded shoulders
(This definition is cited from Wordsmith: An Educational Dictionary-Thesaurus: http://www.wordsmyth.net/cgi-bin/simplesearch.cgi?matchent=zoot+suit&matchtype=exact&matchid=-1&retall=1.)