The Collaborative International Dictionary of English v.0.48:

flat-top \flat-top\ flat-topped \flat-topped\adj.
   1. having a flat or flattened upper surface.
      [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

flattop \flat"top`\ n. (Mil.)
   An aircraft carrier.
   [PJC] Flatulence

WordNet (r) 3.0 (2006):

flat-top
    adj 1: having a flat or flattened upper surface [syn: flat-
           topped, flat-top]