What are the Two Words?

A very nice old lady had a few words to say to her granddaughter.

My dear, said the old lady, I wish you would do something for me.

 I wish you would promise me never to use two words. One is ‘lousy’ and the other is ‘swell’.

Would you promise me that?

Why, sure, Granny, said the girl.

What are the two words?