whacker

whack +‎ -er

• IPA^(key): /ˈwækə(ɹ)/, /ˈʍækə(ɹ)/

whacker (plural whackers)

1. One who, or something which, whacks.
   • 1963, George Blaikie, Scandals of Australia's Strange Past, Adelaide: Rigby Limited, page 117:

     Joe was just about the best Australian heavyweight at the time, a very tough customer in his own right. He didn't have any science, but he was a mighty whacker.

2. (informal) Synonym of whopper (“anything large”)
3. (informal) Synonym of whopper (“an outrageous or blatant lie”)
   • 1908, Morley Roberts, “The Captain of the Ullswater”, in The Blue Peter:

     But all the while Captain Amos Brown was telling whackers that would have done credit to Baron Munchausen, he was really thinking of how he was to save those whose passage to a port not named in any bills of lading looked almost certain.

• Packer whacker
• weed whacker, weedwhacker

• John Camden Hotten (1873) The Slang Dictionary