Mid 17th century; earliest use found in Henry Jeanes (1611–1662), Church of England clergyman. From post-classical Latin suppositalis from classical Latin suppositum + -ālis.
Definition of supposital in US English:
supposital
adjectivesəˈpɒzɪtl
Philosophy
Of or relating to a supposite or suppositum.
Origin
Mid 17th century; earliest use found in Henry Jeanes (1611–1662), Church of England clergyman. From post-classical Latin suppositalis from classical Latin suppositum + -ālis.