When it comes to synonyms of quiddity, the Q's have it. Consider quintessence, a synonym of the "essence of a thing" sense of quiddity (this oldest sense of quiddity dates from the 14th century). Quibble is a synonym of the "trifling point" sense; that meaning of quiddity arose from the subtler points of 16th-century academic arguments. And quirk, like quiddity, can refer to a person's eccentricities. Of course, quiddity also derives from a "Q" word, the Latin pronoun quis, which is one of two Latin words for "who" (the other is qui). Quid, the neuter form of quis, gave rise to the Medieval Latin quidditas, which means "essence," a term that was essential to the development of the English quiddity.
for all of her quiddities, she is a very wise and generous lady Rembrandt's genius was his unparalleled ability to render a person's quiddity in a single portrait.
Recent Examples on the WebTeffi bids us to accept the mystery of this strange business of life in all its delightful quiddity. Sara Wheeler, WSJ, 23 Apr. 2021 None of these quiddities has much to do with efficient military training. Steele Brand, Time, 20 Sep. 2019 Our skulls are like space helmets; we are trapped in our heads, unable to convey the quiddity of our sensations. Jason Pontin, WIRED, 16 Apr. 2018 But not even there, Lawrence thought, could Cézanne entirely overcome convention—Hortense still being somewhat of an image as opposed to sheer quiddity. Rachel Aviv, The New Yorker, 21 Feb. 2011
Word History
Etymology
Middle English quidite, from Medieval Latin quidditat-, quidditas essence, from Latin quid what, neuter of quis who — more at who