The crossword solution for the term 'NINNY'S LACK' is 'SENSE', which is a five-letter word. SENSE is an ability to perceive, understand, and judge things, especially with regard to moral principles. It is often used to refer to common SENSE, which is the ability to think and behave in a reasonable way and to make good decisions. People who lack SENSE are often referred to as ninny's, which is an old-fashioned term for someone who is foolish or silly.