This is an adjective. It is a synonym - at least in SouthYorkshire - for large, big, massive, huge, colossal, gigantic, etc. It is often used in a superlative manner.
"The stone that you threw at my head was macka'"
"He threw a mack-off stone at my head."
1. A versatile adjective for anything that is extreme
2. Noun, a fat person
3. Adjective for when you feelfat
1. This cheeseburger is macka awesome OR you are a macka loser 2. Dude, that chick was such a macka its disgusting
3. I'm feeling macka today, my jeans wont fit
When the weed that you are smoking is poor, you are known as a "Macka ChongaCunt".
Big man - "Charlie, what you smoking there mate?"
Charlie - "Bit of ched pal"
Big man - "awww you Macka Chonga Cunt, get on this purp haze bro"
Charlie - "Safe my G" *Throws ched away*