The very essence of; the inherent nature of something or someone.
Late Middle English: from medieval Latin quidditas, from Latin quid ‘what’.
“It is the quiddity of a shark to harm those in its territory.”
“It’s just part of his quiddities and quirks.”
Nothingburger (noun) (Chiefly US)
A person or thing of no importance, value, or substance. Now esp.: something which, contrary to expectations, turns out to be insignificant or unremarkable.
1950s: from nothing and burger. Added to the OED October 2018.