(~s)
1.
A ~ is a false idea.
I was under the ~ that he intended to marry me.
N-COUNT: usu with supp
2.
Delusion is the state of believing things that are not true.
This was not optimism, it was ~.
N-UNCOUNT
3.
If someone has ~s of grandeur, they think and behave as if they are much more important or powerful than they really are.
PHRASE disapproval