Generalized sense of "express in words" is from 1690s. In a physical sense, "to join, to attach by joints," it is attested from 1610s. Earlier sense "to set forth in articles" (1560s) now is obsolete or nearly so. Related: Articulated; articulating.
It forms all or part of: adorn; alarm; aristarchy; aristo-; aristocracy; arm (n.1) "upper limb of the body;" arm (n.2) "weapon;" armada; armadillo; armament; armature; armilla; armistice; armoire; armor; armory; army; art (n.) "skill as a result of learning or practice;" arthralgia; arthritis; arthro-; arthropod; arthroscopy; article; articulate; artifact; artifice; artisan; artist; coordination; disarm; gendarme; harmony; inert; inertia; inordinate; ordain; order; ordinal; ordinance; ordinary; ordinate; ordnance; ornament; ornate; primordial; subordinate; suborn.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit irmah "arm," rtih "manner, mode;" Armenian arnam "make," armukn "elbow;" Greek arti "just," artios "complete, suitable," artizein "to prepare," arthron "a joint;" Latin ars (stem art-) "art, skill, craft," armus "shoulder," artus "joint," arma "weapons;" Old Prussian irmo "arm;" German art "manner, mode."
early 15c., "a joint or joining; setting of bones," from Old French articulation, from Medieval Latin articulationem (nominative articulatio) "separation into joints," noun of action from past-participle stem of articulare "to separate (meat) into joints," also "to utter distinctly," from articulus, diminutive of artus "joint" (see article). Meaning "the uttering of articulate sounds" is from 1610s.