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1.
-noun
A fist bump of awesomeness and encouragement.
-verb (without an object)
The act of fist bumping to show excitement or achievement. To take part in a fist bump with another person for their excitement or achievement.
-verb (with an object)
To tap a person or object encouragingly with your fist.

Other interpretations.
Can also be considered snide or suggestive in the rigght context.
And he gently knucklefusted him on the shoulder to let him know he did well.
by TheBlueSalmon July 29, 2011