En masse is a phrase that denotes a group or collective action. There exist several synonyms that can be used interchangeably with the phrase, en masse. Some of them include in bulk, collectively, together, all at once, at a stretch, and simultaneously. These synonyms accurately convey the same meaning as en masse, which refers to something that is done by all members of a group or a crowd. They can be used to communicate a similar expression when the idea of a group or an entire population undertaking a task is to be emphasized. In conclusion, these synonyms offer a range of options for replacing en masse while conveying the same meaning.