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 pubic hair piece. A toupee for the pubic area/genitals. In the 1700’s when mercury was used to treat sexually transmitted diseases (Gonorrhea or Syphilis) one of the side effects was the loss of pubic hair. To disguise this condition, that was not cured by mercury, a Merkin was employed.

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