Dictionary.com
definitions

stonker

[stong-ker]
verb (used with object) Australian Informal.
  1. to hit hard; knock unconscious.
  2. to defeat decisively.
  3. to baffle; confuse.

Origin of stonker

First recorded in 1910–15; origin uncertain
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018