The term 'boastful one' can be described by three crossword solutions: GASSY (5 letters), VAUNTING (8 letters), and GASCON (6 letters). GASSY is an adjective meaning 'given to empty boasting or bragging'. VAUNTING is an adjective meaning 'characterized by or given to pretentious or boastful talk'. GASCON is a noun referring to a person from the Gascony region of France, historically known for their boastful behavior. Therefore, the term 'boastful one' can be described as someone who is prone to empty boasting, pretentious talk, and behavior similar to that of people from the Gascony region of France.