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