antiaircraft

from WordNet (r) 3.0 (2006)

antiaircraft
    adj 1: designed for defense from a surface position against air
           attack
    n 1: artillery designed to shoot upward at airplanes [syn:
         {antiaircraft}, {antiaircraft gun}, {flak}, {flack}, {pom-
         pom}, {ack-ack}, {ack-ack gun}]

from The Collaborative International Dictionary of English v.0.48

anti-aircraft \an`ti-air"craft\, a.
   designed for or used for defense against attack by aircraft;
   as, anti-aircraft cannon.
   [PJC]

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