The term 'ACT FOR' can be summarized by two crossword solutions: SUBSTITUTE (10 letters) and REPRESENT (9 letters). SUBSTITUTE means to take the place of someone or something else, while REPRESENT means to stand in for someone or something else. Both terms imply that one person or thing is taking the place of another, either temporarily or permanently. This could be in a professional or personal capacity, such as a lawyer representing a client in court or a friend substituting for a family member at a special event.