Hefty is a term used in Glasgow, mainly the rough area of Pollok.
Hefty generally means, large, huge, big, very, alot.
It is generally used to describe a large object or something similar.

The word Heavy in these areas can also mean the same, as does Pure and are commonly found in the same sentance.

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

Heavy, bulky

A Pollok term meaning large, a lot, very. Actually coming to think about it nobody has a f*cking clue what hefty actually means

Might come from the german "heftig", which means massive or intense.

A very large penis.

meaning your a little bit large around the middle
ie Fat