The phrase "put arm on" is a colloquial expression which means to physically touch or make contact with another person using your arm. There are several synonyms for this phrase such as "place hand on", "grab hold of", "embrace", "clasp", or "wrap around". Depending on the context, other appropriate synonyms might include "hug", "hold", "grasp", "seize", or "grip". Each of these words has slightly different connotations and levels of intimacy. For example, "hug" implies a warmer, more affectionate gesture, while "seize" might indicate a more aggressive or hostile action. In general, choosing the right synonym for "put arm on" depends on the tone of the situation and the desired level of physical contact.