look up any word:
1. big un
big un: a girl that is big or overweight. cane from the magazine big uns. but big un translates to a girl that is just big! and not a girl with big uns (breast size)
look at that girl crossing the road (fat) shes a big un
2. big un
A lad who has gone through puberty earlier than his peers and is taller and looks more dominant in comparison
You've shot up to be a big un my son
rss and gcal