A person with whom one shares a rental property, not necessarily a flat.(noun)
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Use "flatmate" in a sentence
"And my (as in flatmate's) new boyfriend was sitting there quietly?"
"My dear previously-non-gamer flatmate is now an SSX addict after seeing it play."
"Other results that may have you calling your flatmate/partner/granny in to see the action are: Glasgow Govan, TEL, Argyll & Bute, Edinburgh Central and of course Gordon, not to mention about 40 more!"