WordNet (r) 3.0 (2006):

flak
    n 1: a slick spokesperson who can turn any criticism to the
         advantage of their employer [syn: flak catcher, flak,
         flack catcher, flack]
    2: intense adverse criticism; "Clinton directed his fire at the
       Republican Party"; "the government has come under attack";
       "don't give me any flak" [syn: fire, attack, flak,
       flack, blast]
    3: artillery designed to shoot upward at airplanes [syn:
       antiaircraft, antiaircraft gun, flak, flack, pom-
       pom, ack-ack, ack-ack gun]

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "flak":
   abuse, adverse criticism, aggressiveness, animadversion,
   antiaircraft fire, artillery, aspersion, bad notices, bad press,
   battery, bellicosity, belligerence, bickering, blame, cannon,
   cannonry, captiousness, carping, cavil, caviling, censoriousness,
   censure, coast artillery, combativeness, complaints, condemnation,
   contentiousness, criticism, cross fire, curtain fire, direct fire,
   disapprobation, disapproval, dissension, dissent, dissidence,
   dry fire, exception, faction, factiousness, faultfinding,
   field artillery, file fire, fire, fire of demolition, firepower,
   fireworks, firing, flack, ground fire, gunfight, gunfire, gunplay,
   hairsplitting, heavy field artillery, high-angle fire, hit,
   home thrust, horizontal fire, hostile criticism, hypercriticalness,
   hypercriticism, imputation, infighting, interdiction fire,
   irascibility, irritability, knock, litigiousness, machine-gun fire,
   mortar fire, musketry, nagging, niggle, niggling, nit, nit-picking,
   obloquy, ordnance, overcriticalness, partisan spirit, partisanship,
   percussion fire, pestering, pettifogging, pistol fire,
   priggishness, pugnacity, quarrelsomeness, quibble, quibbling,
   raking fire, rap, rapid fire, reflection, reproachfulness,
   ricochet fire, rifle fire, shellfire, shoot-out, shooting,
   shrewishness, siege artillery, siege engine, slam, stricture,
   swipe, taking exception, time fire, trench artillery,
   trichoschistism, vertical fire, zone fire