The term 'ungregarious one' can be defined as a LONER, which is a person who prefers to be alone and avoids social interaction. This term is often used to describe someone who is introverted or shy, and who does not enjoy being around large groups of people. It can also refer to someone who is solitary by choice, such as a hermit or recluse. In the context of a crossword puzzle, the term 'ungregarious one' can be solved with the word 'LONER, ' which has five letters.