different between whopper vs whacker

English

whop +? -er

whopper (plural whoppers)

(informal) Something remarkably large.
- 1939, Noel Langley, Florence Ryerson, Edgar Allan Woolf, The Wizard of Oz
  There's a storm blowing up, Sylvester — a 'whopper', speaking in the vernacular of the peasantry.
(informal) An outrageous or blatant lie.

whack +? -er

whacker (plural whackers)

One who, or something which, whacks.
(informal) Synonym of whopper (“anything large”)
(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.

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