(~s)
1.
An ~ is a false idea or belief.
No one really has any ~s about winning the war.
= delusion
N-VAR: oft N that, N of n/-ing
2.
An ~ is something that appears to exist or be a particular thing but does not actually exist or is in reality something else.
Floor-to-ceiling windows can give the ~ of extra height...
N-COUNT: oft N of n/-ing