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 (wăm′ō, hwăm′ō)
interj. Slang
Used to indicate the startling abruptness of a sound, action, or event: "The alarm goes off and—whammo!—we're all at our assigned stations" (Meg Greenfield).

[Alteration of wham.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


a variant form of wham2
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in periodicals archive ?
First pass in to Bergkamp from Parlour - and whammo! The Ivorian cleaned Arsenal's best player right out.
They mention two straightforward things and then, whammo, the third one shatters the pattern.
I didn't mean him any harm, and whammo! He bit me right in the leg!
WHAMMO! No, Winnie the Pooh never had majesty, but boy he had nous.
Her newly named Cable Entertainment Group accounts for a whammo 50% of NBCUniversal's cash flow.
The enemy disappears behind a hillock half a kilometer away and you desperately keep your fingers crossed as the mortar follows suit, a heart-stopping moment later, WHAMMO! A massive green explosion and debris from the enemy's body gently descends to the ground as your teammates glide up to your flag and return it to its stand.
A perfectly fine day was going swell when - whammo - some situation flipped the world upside down.
Whammo! The emperor was found to have no clothes, everyone panicked, there was literally a run on the bank, and, as Fortune put it, a major counterparty went bust and dragged down others to whom it was linked.
Whammo. Irony can't be gone around, it can only be gone through." (APR, May/June 2008.)
A savage squall came across her track and pushed her to 61 knots--then 'whammo', it was all over!
Every blow began with an extended wind up, the impact punctuated by a "whammo" sound effect, and once hit, the victim, hand to face, spun erratically in place.
These entities let everything ride for a year at a time, then WHAMMO, they hit us with their bills all at one whack, with nary a thought of offering even the slightest glimmer of an idea of what we got for our money.