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1.
A US Navy wife who fucks around with other men while her man is out on deployment. Named for the West Pacific, or WestPac cruise, which is a common and lengthy deployment for West Coast sailors.
"Dude, don't fuck with those WestPac widows or you're liable to end up with a shotgun pointed at you."
by Mister Priapus June 01, 2005
 
2.
Originally a women whose husband is at sea on a wetpac (western pacific) cruise for 6-9 months with the US Navy. Now more liberally applied to any women whose husband is at sea any where for any amount of time.
"Hey Joe! Wanna a hot date tonight? There a bunch of westpac widows down at the Silver Saddle!"
by River Rat August 22, 2005