Meaning

noun the state of being included

noun the relation of comprising something

noun any small intracellular body found within another (characteristic of certain diseases)

originBorrowed from Latin inclusio, inclusionis, from the verb Latin inclūdō (“to shut in, enclose, insert”), from in- (“in”) + claudō (“to shut”), ultimately from Proto-Indo-European *kleh₂u- (“key, hook, nail”). By surface analysis, include + -sion. Doublet of enclosure.

Etymology from Wiktionary, CC BY-SA 3.0