no fear

Etymology
The opposing senses of the interjection derive from the phrase functioning as an ellipsis of both   ("be assured") and        ("it's impossible").

Prepositional phrase

 * 1) Not a chance, impossible.

Interjection

 * : no worries, don't worry.
 * : absolutely not.
 * : absolutely not.
 * : absolutely not.

Usage notes
The two senses of the phrase are more or less antonymic: one can express a desire for something to proceed, while the other usually expresses a desire for something not to proceed. Since the phrase is a contranym, care should be taken to avoid ambiguity or confusion.