The term LIKE A DULL KNIFE can be summarized by the crossword solution BLUNT, which is a five-letter word. The term LIKE A DULL KNIFE is an idiom that is used to describe something that is not effective or efficient. It is often used to describe someone who is not very sharp or quick-witted. The term is derived from the fact that a dull knife is not as effective as a sharp one when it comes to cutting or slicing.