Synonyms for Flak (same or very similar meaning)
WordNet sense 1 (a slick spokesperson who can turn any criticism to the advantage of their employer):
flack, flak catcher, flack catcherWordNet sense 2 (intense adverse criticism):
attack, blast, fireWordNet sense 3 (artillery designed to shoot upward at airplanes):
antiaircraft, ack-ack, pom-pom, ack-ack gun, antiaircraft gunFrom the ODE community, based on WordNetadd/edit