"Good right arm" is a phrase often used to describe someone who possesses excellent skills or capabilities with their dominant arm. However, there are several synonyms you can use to describe such a person. For example, you could say they have a "strong right arm," "powerful right arm," "skilled right arm," "dominant right arm," "expert right arm," or "gifted right arm." These phrases all convey a similar meaning to "good right arm" but with slightly different nuances. Whether you're describing an athlete, musician, or artist, using these synonyms can add variety and richness to your language.