The phrase "power arm" can be used to describe a strong and effective limb, but it also has many synonyms that can enhance your writing. Depending on the context, you could use alternatives like "mighty arm," "dominant limb," "strength appendage," or "forceful extremity." Other possible synonym options include "potent arm," "vigorous limb," "commanding appendage," or "robust extremity." Choosing the right synonym for "power arm" can add variety and interest to your writing, while also providing a more descriptive and accurate portrayal of the subject.