intergradation

noun

in·​ter·​gra·​da·​tion ˌin-tər-grā-ˈdā-shən 

-grə-

: the condition of an individual or population that intergrades

intergradational

ˌin-tər-grā-ˈdā-sh(ə-)nəl 

-grə-

adjective

Word History

First Known Use

1874, in the meaning defined above