marginal modal auxiliary

marginal modal auxiliary: a verb which carries the same kind of meaning as one of the modal auxiliaries. Marginal modal auxiliaries can be used either as auxiliaries (e.g. without do-insertion in interrogative and negative sentences), or as catenatives. Marginal modal auxiliaries are dare, need, have to, used to. They can express either root or epistemic meaning, and have both finite and non-finite forms.