From Wiktionary, the free dictionary
From flat + sharer.
flatsharer (plural flatsharers)
- A person who shares a flat (apartment).
2015 October 2, Hilary Osborne, “Cost of flatsharing in UK's priciest towns rises by 30% in three years”, in The Guardian[1]:The average amount asked of flatsharers in the capital has increased by nearly 14% since 2012, to £692 a month, or £8,300 a year.