"antiaircraft" in the noun sense
1. antiaircraft, antiaircraft gun, flak, flack, pom-pom, ack-ack, ack-ack gun
artillery designed to shoot upward at airplanes
"antiaircraft" in the adjective sense
1. antiaircraft
designed for defense from a surface position against air attack
Source: WordNet® (An amazing lexical database of English)
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