from
The Collaborative International Dictionary of English v.0.48
Whap \Whap\, Whop \Whop\, v. i. [Cf. OE. quappen to palpitate,
E. quob, quaver, wabble, awhape, wap.]
To throw one's self quickly, or by an abrupt motion; to turn
suddenly; as, she whapped down on the floor; the fish whapped
over. --Bartlett.
[1913 Webster]
Note: This word is used adverbially in the north of England,
as in the United States, when anything vanishes, or is
gone suddenly; as, whap went the cigar out of my mouth.
[1913 Webster] Whap