Unconceivable and Unthought-of

Unconceivable adjective - Too extraordinary or improbable to believe.

Unthought-of and unconceivable are semantically related. In some cases you can use "Unthought-of" instead an adjective "Unconceivable".

Unthought-of adjective - So unexpected as to have not been imagined.

Unconceivable and unthought-of are semantically related. Sometimes you can replace term "Unconceivable" with "Unthought-of", this terms are similar.