The crossword solutions for the term SOLID, FIRM are HARD, which is a four-letter word. The term 'HARD' is an adjective that is used to describe something that is solid and firm. It is often used to describe objects that are difficult to break or bend, such as rocks or metals. It can also be used to describe something that is difficult to do or understand, such as a HARD math problem. In general, the term 'HARD' implies something that is strong and unyielding.