<philosophical terminology> in the traditional square of opposition, the relationship between a universal proposition and its corresponding particular proposition. Thus, an I is the subaltern of its A proposition, and an O is the subaltern of its E proposition. Thus, for example: "Some larks are birds is subaltern to All larks are birds", and "Some robins are not fish is subaltern to No robins are fish". Subalternation is a reliable pattern of inference only on the assumption of existential import for universal propositions.
[A Dictionary of Philosophical Terms and Names]
Try this search on OneLook / Google