1960s, probably an alteration of pussy (n.2). DAS suggests shortened from hypothetical pussy-wussy, reduplicated form of pussy (n.1).
*wrād-
wunderkind
Wurlitzer
wurst
wuss
wussy
wuthering
wyandotte
wych
wynn
Wyoming
)window.location='https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=byronic106@yahoo.com&lc=US&item_name=Donation+to +Help+Keep+Etymonline+Free+and+Open&no_note=0&cn=&curency_code=USD&bn=PP-DonationsBF:btn_donateCC_LG.gif:NonHosted'){kind=link}