Its a board game, involving 3-8 players, based on the game pictionary. In pictionary, you try to draw a certain word within a time limit, and without speaking, others are trying to guess it. BUT in the case of this game, it involves marijuana, and the time limit is how long you can hold the hit of smoke in your lungs.
Pictionary is derived from the words "picture" and "dictionary"; Hitionary is just a playing on the name of the real, but sober game, and instead of "pic" its "hit".
-"Shit u want to play an interesting game?"
-"fuck yea man! it better be good tho, mfker!"
-"Dude wtf is hit-tionary?!?!"
-"Just grab your bowl dude"