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1.
Briefly and rapidly masturbating a quasi-erect penis (or "semi") after foreplay leading to partner sex. In this usage the goal is not to masturbate to orgasm, but merely to get the penis stiff enough to penetrate vagina or anus under the assumption that the erection will stay sufficient throughout intercourse aka fucking, presumably leading to a successful climax (orgasm).
"I had to jack it up a little before I could go in, but I was afraid she'd think it was kind of gay, or that I didn't love her."

"Naw, man, you do what you gotta do. Go ahead and get it up a little more. If Dorothy has a problem with that, then why doesn't she use HER hand?"
by al-in-chgo February 20, 2010
9 2
 
2.
jack off
i might need to jack it up later
by alfalfa123456789 November 25, 2009
10 7