The term 'Terrible Twos, For One' is a phrase used to describe the period of time in a child's life when they are two years old and are beginning to assert their independence. This period is often characterized by tantrums, defiance, and other challenging behaviors. The crossword solutions for this term are 'PHASE, ' which is a five-letter word. PHASE is a term used to describe a stage or period in the development of something, such as a child's development. In this case, it is referring to the PHASE of development that children go through when they are two years old.