Originally used in first person shooter games to describe shooting another players head. Can be used to describe the act owning in an activity in general(doesn't HAVE to be a headshot if its good enough ownage)
As a verb, I totally domesnaxed that mother fucker when he peaked Long A.
As a adjective, Wow man that was so domesnax, he couldn't do anything but die when you saw him.
As a noun*witnessing or enducing a headshot/ownage of somebody" (DOMESNAXXXXXX!!)
"Give him the snax, I think hes hungry"