granny flat
n.— «One of the two barn-like structures that until recently still stood in the English countryside now forms a four-car garage with upstairs servants’ quarters, guest house or teen room. (The builders also suggest it would make an ideal granny flat.)» —“House leaps thre centuries and an ocean” by Robert Sheppard Globe and Mail (Toronto, Can.) Jan. 23, 1978. (source: Double-Tongued Dictionary)