"Muck in" is a colloquial phrase that means to join in and work alongside others, often in a team or collective effort. This phrase has several synonyms that can be used interchangeably such as "pitch in," "lend a hand," "help out," "assist," "get involved," and "contribute." All these verbs connote the willingness to work with others to achieve a common goal. They are often used in social or community contexts where individuals come together to offer their resources and expertise for a worthy cause. By using these synonyms, one can effectively express their willingness to be a team player, take an active role in group activities and contribute to the overall success of a project.