GNU Collaborative International Dictionary of English

Found one definition

1.       
   Megalopolis, Megapolis (mĕgˌȧ‑lŏpˈṓ‑lĭs), n. [NL., fr. Gr. μεγαλόπολις; μέγας, μεγάλη, great + πόλις city.]
   1. A chief city; a very large cuity; a metropolis.
   
   [1913 Webster]
   
   
   2. A region in which the suburbs of several large cities merge to form one large predominantly urbanized area.
   
   [PJC]