Vagary comes from Latin vagārī ('to wander, roam'), from vagus ('wandering, roving'); originally meaning a wandering journey, later a wandering of the mind or an erratic notion. In current use it is a noun meaning "an unpredictable or erratic action, notion, or change". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. The historical chain includes Latin vagārī and Latin vagus. Related English forms include vagrant, vagabond, vague, and vagrancy. The semantic development is therefore important as well as the form: the word moves from the older concrete, technical, or literal setting into the present figurative or specialized sense.