It should be hyphenated (with two Ms). Someone who shares are room, e.g. in a student dorm. Often used to mean the same as flatmate (i.e. not necessarily in the same room, but sharing the same dwelling). ... The use of hyphens tends to gradually drop away in compound terms, hence the apparently more common use of roommate.

Is roommate all one word?

In the UK, the term "roommate" means a person living in the same bedroom, whereas in the United States and Canada, "roommate" and "housemate" are used interchangeably regardless whether a bedroom is shared, although it is common in US universities that having a roommate implies sharing a room together.

Is roommate a compound word?

Roommate, on the other hand, is a word from Modern English and is indeed a compound word 'room' + 'mate'.