The term 'OPPOSITE of PRO' can be summarized by two crossword solutions: ANTI (4 letters) and CON (3 letters). ANTI is a prefix derived from the Greek word 'ANTI, ' meaning 'AGAINST' or 'OPPOSITE.' CON, on the other hand, is an abbreviation of the Latin word 'CONTRA, ' which also means 'AGAINST' or 'OPPOSITE.' Both terms are used to describe something that is the OPPOSITE of something else. In this case, they are used to describe something that is the OPPOSITE of 'PRO, ' which means 'in favor of.' Therefore, the OPPOSITE of 'PRO' can be described as 'ANTI' or 'CON.'