primogeniture

UK: /ˌpraɪməʊˈdʒɛnɪtʃə/ US: (prī′mə jen′i chər, -chŏŏr′)

WordReference Random House Unabridged Dictionary of American English © 2025

pri•mo•gen•i•ture  (prī′mə jen′i chər, -chŏŏr′), n. 

1. the state or fact of being the firstborn of children of the same parents.
2. Law the system of inheritance or succession by the firstborn, specifically the eldest son. Cf. postremogeniture. 

• Medieval Latin prīmōgenitūra a first birth, equivalent. to Latin prīmō at first + genitūra, equivalent. to genit(us) (past participle of gignere to beget; see kin) + -ūra -ure
• 1585–95

pri′mo•gen′i•tar′y, pri′mo•gen′i•tal, adj. 
pri′mo•gen′i•ture•ship′, n. 

Collins Concise English Dictionary © HarperCollins Publishers::

primogeniture / ˌpraɪməʊˈdʒɛnɪtʃə/ noun

1. the state of being a first-born
2. the right of an eldest son to succeed to the estate of his ancestor to the exclusion of all others
   Compare ultimogeniture

Etymology: 17th Century: from Medieval Latin prīmōgenitūra birth of a first child, from Latin prīmō at first + Late Latin genitūra a birth

primogenitary / ˌpraɪməʊˈdʒɛnɪtərɪ -trɪ/ adjective