quiddity
/ˈkwɪdətɪ/noun
(pl. -ies)［mass noun］
1- chiefly Philosophy the inherent nature or essence of someone or something【主哲】（人或事物的）本质, 实质。
1.1
- count noun a distinctive feature; a peculiarity显著特点; 特性, 怪癖：
his quirks and quiddities.
他的多种怪癖。
词源
late Middle English: from medieval Latin quidditas, from Latin quid 'what'.