The answer to the crossword puzzle for the term 'OPPOSITE OF SYN' is ANT (3 letters). The word 'ANT' is a noun that refers to a small insect that lives in colonies and is known for its hard work and cooperation. It is also used as an adjective to describe something that is opposite or contrary to something else. In this case, the opposite of syn would be ANT, meaning something that is not in agreement or harmony with something else.