Definition of primogeniturist in US English:

primogeniturist

noun

rare
  • A person who believes that the right of succession or inheritance belongs to the firstborn.

Origin

Mid 19th century. From primogeniture + -ist.

Pronunciation

primogeniturist

/ˌprʌɪmə(ʊ)ˈdʒɛnɪtʃ(ə)rɪst/