idiosyncrasy

UK: /ˌɪdiəʊˈsɪŋkrəsi/

US: /ˌɪdiəˈsɪŋkrəsi, -ˈsɪn-/

US: (id′ē ə sing′krə sē, -sin′-)

Inflections of 'idiosyncrasy' (n): npl: idiosyncrasies

WordReference Random House Learner's Dictionary of American English © 2025

id•i•o•syn•cra•sy /ˌɪdiəˈsɪŋkrəsi, -ˈsɪn-/   n. [countable] , pl. -sies. 

1. a characteristic, a habit, a particular like or dislike, etc., special to or distinctive of an individual:
   a few little idiosyncrasies, like wearing earmuffs inside and outside on cold days.

id•i•o•syn•crat•ic /ˌɪdioʊsɪnˈkrætɪk, -sɪŋ-/  adj.: 

her idiosyncratic ways.

WordReference Random House Unabridged Dictionary of American English © 2025

id•i•o•syn•cra•sy  (id′ē ə sing′krə sē, -sin′-), n., pl. -sies. 

1. a characteristic, habit, mannerism, or the like, that is peculiar to an individual.
2. the physical constitution peculiar to an individual.
3. Physiology, Psychology a peculiarity of the physical or the mental constitution, esp. susceptibility toward drugs, food, etc. Cf. allergy (def. 1).

Also, idiocrasy. 

• Greek idiosynkrāsía, equivalent. to idio- idio- + syn- syn- + krâs(is) a blending + -ia -y³
• 1595–1605;

id•i•o•syn•crat•ic  (id′ē ō sin krat′ik, -sing-), adj.  id′i•o•syn•crat′i•cal•ly, adv. 
Synonyms

• 1. peculiarity, quirk. See eccentricity. 

Collins Concise English Dictionary © HarperCollins Publishers::

idiosyncrasy / ˌɪdɪəʊˈsɪŋkrəsɪ/ noun ( -sies)

1. a tendency, type of behaviour, mannerism, etc, of a specific person; quirk
2. the composite physical or psychological make-up of a specific person
3. an atypical reaction of an individual to specific foods, drugs, or other agents

Etymology: 17th Century: from Greek idiosunkrasia, from idio- + sunkrasis mixture, temperament, from sun- syn- + kerannunai to mingle