From Latin 'includere' (to shut inside) — to include is literally to close something within the group.
Definition
To contain as part of a whole; to make part of a group or set; to regard or treat as part of a category.
The Full Story
Latin15th centurywell-attested
From Latin 'inclūdere' (to shut in, to enclose, to insert), composed of 'in-' (in, into) and 'claudere' (to shut, to close). The PIE root is *kleh₂u- (hook, peg, crooked or forked branch — used for fastening or barring a door). The original sense was emphatically physical: to shut something inside a walled enclosure or lockedcontainer. By the 1st century CE, Cicero and
Did you know?
The word 'include' originally meant 'to physically shut something inside' — like locking a prisoner in a cell. The modern sense of 'contain as part of a group' is a metaphor: to include someone is to close them inside the circle. The opposite, 'exclude,' means to close them outside it.
), 'claustrum' (a bolt, an enclosure — whence 'cloister' and 'claustrophobia'), and Greek 'kleís' (key, collarbone — whence 'clavicle'). To include something is, at its deepest root, to lock it inside. Key roots: claudere (Latin: "to shut, to close"), in- (Latin: "in, into"), *klāu- (Proto-Indo-European: "hook, peg, crooked branch (used for fastening)").