The Oxford English medical definition states: Blunt lung occurs when a person has been smoking blunts for a long period of their life. All of the blunts they have consumed begin to add up and create a persistent cough that can only go away if the user decides to stop smoking blunts, which is highly unlikely because blunts make the world go round.
Timmy: (cough) (cough)
Jimmy: Timmy are you okay? That cough doesn't sound too good.
Timmy: Yeah, I'm fine. I just have a case of blunt lung from all those fat ass blunts I burn.