The opposite of weakling.
A strong and resilient person despite their appearance and attitude.
M: All you did was a day of decorating - you're such a weakling!
D: Actually I painted seven doors, skirting, all the wood, the floor and the wall. I AM TOUGHLING
M: He is so small and weak, look at him.
J: Actually he is a black belt karate champ
M: Wow, what a toughling.