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4.
Shortened version of definitely. Often used by teens.
A: "Look at that"
B: "That's cool"
C: "Deffy"
by Sarah June 28, 2004
 
1.
Large boobs by default on a fat girl.
"Megan has huge melons, but they're deffies"
by John Eysman July 10, 2008
 
2.
Slang for "definition".
Yo teach, what's the deffy of "missile tits"?
by Meo Bets@ June 28, 2006
 
3.
definitely, totally, absolutely, with certainty (adv.)
We should deffies go to the movies later.

Note: In most situations, deffies can be substituted for totes or probs to add an extra sprinkle of awesome sauce to your sentences.

Also note that deffies is not a derogatory term for a group of multiple people with extremely poor hearing.
by Suz! :) November 09, 2010
 
5.
To make an emberassment of oneself. To fail at suicide in an attempt of gaining attention.
Deffy slit his wrists like a little school girl.
by Anonymous October 02, 2003