The Collaborative International Dictionary of English v.0.48:

Cockloft \Cock"loft`\ (?; 115) n. [Prop., a loft where cocks
   roost.]
   An upper loft; a garret; the highest room in a building.
   --Dryden. Swift.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cockloft
    n 1: a small loft or garret