Learner's definition of NASTY
[also more nasty; most nasty]
1 : very unpleasant to see, smell, taste, etc. 2 : indecent and offensive 3 : unpleasant and unkind
That was a nasty [=cruel, mean] trick!
That nasty old man yelled at me just for stepping on his lawn!
He sent a nasty letter/e-mail to the company.
She's got quite a nasty temper/disposition.
He said lots of downright nasty things about her.
She called him a few nasty names and left.
4 : very bad or unpleasant
It's rainy and nasty outside.
I've got a really nasty problem.
He's in for a nasty surprise when he gets home.
He just went through a nasty divorce.
a nasty legal battle
Their relationship got/turned nasty soon after they were married.
5 : very serious or severe : causing much damage