a. Pertaining to the infinite mood. “Infinitival stems.” Fitzed. Hall. [ 1913 Webster ]

n. [ L. infinitivus: cf. F. infinitif. See Infinite. ] Unlimited; not bounded or restricted; undefined. [ 1913 Webster ]

Infinitive mood (Gram.), that form of the verb which merely names the action, and performs the office of a verbal noun. Some grammarians make two forms in English: (a) The simple form, as, speak, go, hear, before which to is commonly placed, as, to speak; to go; to hear. (b) The form of the imperfect participle, called the infinitive in -ing; as, going is as easy as standing. [ 1913 Webster ]

With the auxiliary verbs may, can, must, might, could, would, and should, the simple infinitive is expressed without to; as, you may speak; they must hear, etc. The infinitive usually omits to with the verbs let, dare, do, bid, make, see, hear, need, etc.; as, let me go; you dare not tell; make him work; hear him talk, etc. [ 1913 Webster ]

☞ In Anglo-Saxon, the simple infinitive was not preceded by to (the sign of modern simple infinitive), but it had a dative form (sometimes called the gerundial infinitive) which was preceded by to, and was chiefly employed in expressing purpose. See Gerund, 2. [ 1913 Webster ]

The gerundial ending (-anne) not only took the same form as the simple infinitive (-an), but it was confounded with the present participle in -ende, or -inde (later -inge). [ 1913 Webster ]

n. (Gram.) An infinitive form of the verb; a verb in the infinitive mood; the infinitive mood. [ 1913 Webster ]

adv. (Gram.) In the manner of an infinitive mood. [ 1913 Webster ]