merismus

Etymology
From, derived from the Ancient Greek verb.

Noun

 * 1)  A metonymic term to describe a type of synecdoche in which two parts of a thing, perhaps contrasting or complementary parts, are made to stand for the whole.

Usage notes
The term was generally used around in the sixteenth and seventeenth centuries. (It can be found used to describe both Shakespeare and Christian Reformation theologians by their contemporaries.) It then seems to have fallen into disuse, only being revived in the middle of the twentieth century.