That minuscule fraction of time it takes your brain to realize that you've just made a GIGANTIC mistake and reconcile the fact that it is too late.
Bob hit send on his email to Tom, only then realizing that he had copied in the entire company on the x-rated pictures of him and his latest conquest swinging from his sex swing in full leather outfits.
The momentary panic that occurs when something irreversible goes wrong. Can also be used to describe something that turns out to be reversible although you were worried at the time it wasn't.
1.Dave sent his girlfriend pictures of himself with another woman, by accident, regretting it an ohnosecond later.
2. I experienced an ohnosecond when i realised my head was stuck between the railings.
The split second between hitting the "send" button on the computer to send an email, and realizing that there is a serious problem with the email (such as using "reply all" instead of reply to sender, especially for an inflammatory email, or seeing a nasty grammatical mistake after the send button has been hit.
I realized in that ohno second that my nasty reply to the corporate email also went to the president and all VPs.
Ohno-second is the period of time that is spent waiting for the debit or credit card you just submitted for payment to respond - hopefully with the word "approved", and hopefully not "payment declined" (Oh No!) The ohno seconds are usually spent mentally reviewing your account balances and recent purchases or date of your automatic deposit. MUCH longer than a nano-second, this word is most appropriate while being at the front of a long line in a store with people looking over your shoulder and the pimple-faced clerk glaring at you as if to say "I know YOU can't afford this purchase, loser".
I started to sweat during the ohno-seconds waiting for my card to be accepted while I was standing in line at WalMart with 50.00 worth of melting Ben & Jerry's! Oh no, did that rent check go through yet?"