The phrase "group action" can refer to various types of collective endeavors, and there are plenty of synonyms to convey its different nuances. For instance, "collaboration" stresses the idea of working together towards a common goal, while "cooperation" underlines the importance of mutual support and assistance. "Joint effort" and "teamwork" both point to the idea of multiple participants pooling their resources and skills. "Coalition," on the other hand, connotes a collaboration between separate groups or factions with differing interests. Other possible synonyms for "group action" might include "collective enterprise," "partnership," "united front," or "concerted action," depending on the specific context.