'article' (base of 'articled') originates from Old French 'article', ultimately from Latin 'articulus', where 'articulus' meant 'a small joint, a separate part' (a diminutive of 'artus' 'joint').

'article' passed from Latin 'articulus' into Old French as 'article', then into Middle English as 'article'; the legal sense 'a particular clause or a written agreement' developed from these uses, and the verb sense 'to bind by articles' (hence 'articled') arose from the practice of formal 'articles' of apprenticeship.

Initially it meant 'a small joint or distinct part' in Latin; over time it came to mean 'a distinct clause or item (an article)' and then gave rise to verbal uses such as 'to state in articles' and 'to bind by articles (apprenticeship)', which is reflected in 'articled'.