The term 'quite substantial' can be described by three crossword solutions: MASSIVE (7 letters), SOLID (5 letters), and EMCEE (5 letters). MASSIVE is an adjective that means very large in size, amount, or degree. SOLID is an adjective that means firmly established, strong, or stable. EMCEE is a noun that refers to a person who acts as a master of ceremonies at a public event. Together, these words describe something that is very large, firmly established, and strong.