The term 'instant of truth' can be summarized as a MOMENT of clarity or realization. It is often used to describe a situation in which a person must make a difficult decision or come to terms with a difficult truth. The crossword solution for this term is 'MOMENT, ' which is a period of time that is typically brief but can also be extended. A MOMENT can be a fleeting instant or an extended period of time, depending on the context.