1a. especially cool, hip, or rad.
b. a shortening/modernization of the phrase "I'm down with that"
2. describing an action which one wishes to immulate because if its percieved esteem in society.
May be intensified with the addition of da- as in
"That music was da-downk"
3. to do something extremely well
She is downking that performance.
Wow that was her performance?