https://www.urbandictionary.com/define.php?term=onosecond&defid=1997335

The horrible moment when you realise that you have accidentally done something very slightly wrong which has very bad (usually embarassing) implications for you. This is typically the moment of realisation that you just sent a dirty text message to a close member of family, typically your mother, rather than the intended recipient.

Message: "i'm free this afternoon so come over and fuck me senseless, my parents will be out all day"
Recipient: Mum
Message Sent
- Onosecond occurs here -