infinitive

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A verb form that functions as a substantive while retaining certain verbal characteristics, such as modification by adverbs, and that in English may be preceded by to, as in To go willingly is to show strength or We want him to work harder, or may also occur without to, as in She had them read the letter or We may finish today.

from The Century Dictionary.

• noun a name conveniently used to designate briefly the infinitive phrase consisting of the infinitive proper (for example, ‘designate,’ below) and the so-called ‘sign,’ the preposition ‘to,’ when separated by a qualifying adverb or phrase, as in ‘to briefly designate,’ ‘to readily understand,’ ‘to suddenly and completely change one's attitude.’ This use is in high disfavor with literary critics and purists who write upon the subject, but it occurs abundantly in English literature from the seventeenth century down. Nearly every ‘standard author’ is ‘guilty’ of it, as Fitzedward Hall and others have shown, and it is thoroughly established in popular speech. It is often dictated by a sense of rhythm, the placing of the adverb after the verb and before the week adjunct or object which follows the verb resulting often in disharmony of rhythm and stress. The idiom is a perfectly natural development of the conditions given—a verb to be qualified, a stress qualifier, and an unstressed syllable (to) of no definite meaning. This syllable to is instinctively treated as a or the is treated in a similarly stressed sequence of adjective and noun (‘a brief designation,’ ‘the proper order,’ etc.)
• In grammar, unlimited; indefinite: noting a certain verb-form sometimes called the infinitive mode. See II.
• noun In grammar, a certain verb-form expressing the general sense of the verb without restriction in regard to person or number, as English give, German geben, French donner, Latin dare, Greek διδόναι.
• noun An endless quantity or number; an infinity.

from the GNU version of the Collaborative International Dictionary of English.

• noun Unlimited; not bounded or restricted; undefined.
• noun (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.
• adverb (Gram.) In the manner of an infinitive mood.
• noun (Gram.) An infinitive form of the verb; a verb in the infinitive mood; the infinitive mood.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun grammar The uninflected form of a verb. In English, this is usually formed with the verb stem preceded by 'to'. e.g. 'to sit'
• noun grammar A verbal noun formed from the infinitive of a verb
• adjective grammar Formed with the infinitive

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the uninflected form of the verb