"Go aboard" is a phrase that refers to getting onto a vehicle or vessel. There are several synonyms for this phrase that can be used depending on the context. "Embark" is a common synonym that implies a journey or adventure. "Board" is another option that is more commonly associated with transportation. "Enter" can also be used if the context is more formal or business-related. "Mount" and "climb aboard" are additional synonyms that are often used in a more casual setting. Overall, the choice of synonym will depend on the tone and context of the sentence, but all convey the idea of getting onto a vehicle or vessel.