n.
   - a large, impressive house.
- 
(mansion block)
 Brit. a large block of flats.
- (in names) a terrace or mansion block:![]()  Carlyle Mansions. 
Etymology
  ME (denoting the chief residence of a lord): via OFr. from L. mansio(n-) ‘place where someone stays’, from manere ‘remain’.