'articling' ultimately derives from English 'article' (as in 'articles' of apprenticeship or agreement), which itself comes from Old French 'article' and Latin 'articulus'.

'articling' developed from the legal usage of 'articles' (a written agreement); the verb sense 'to be articled' (to be bound by articles as an apprentice) arose in English from the noun 'articles' and then produced the participle/gerund 'articling'.

Originally 'articulus' referred to a small joint or a separate item; through Old French and Middle English it came to mean a section, a clause or a written instrument ('article'), and in English the term was extended to mean the contractual apprenticeship ('to be articled' / 'articling').