whacker

noun

1. One who, or something which, whacks.

   “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”).

   “"Oh, there's a whacker!" cried East; "we haven't been within a hundred yards of his barn; we haven't been up here above ten minutes, and we've seen nothing but a tough old guinea-hen, who ran like a greyhound."”

   “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.”

4. (slang)A radio amateur who is keenly interested in emergency response and may travel to the sites of emergencies.