The phrase "putting the arm on" typically means to pressure or coerce someone into doing something, often relating to money or favors. Some antonyms for this phrase could include collaborating, encouraging, supporting, or assisting. These words all connote a sense of positivity and cooperation, rather than the potentially negative and forceful nature of "putting the arm on." Other antonyms could include negotiating, compromising, or finding a mutually agreeable solution, highlighting the importance of respectful communication and working together towards a common goal without resorting to intimidation or manipulation.