Definition of "infinitive"

The MANNERS of acting, in grammar called modes or moods, are four; Infinitive, Imperative, Indicative, Subjunctive or Conjunctive.

1847, J. J. P. Le Brethon, L. Sandier, Guide to the French language; especially devised for persons who wish to study that language without the assistance of a teacher. the tenth edition, revised and corrected, London, page 69

There are four moods, the Infinitive, Imperative, Indicative, and Subjunctive. [...] the Infinitive is used to express a thing in a general manner.

1857, Henry Tindall, A grammar and vocabulary of the Namaqua-Hottentot language, page 38

INFINITIVE MOOD or MANNER.To Have, Avoir.

1847, J. J. P. Le Brethon, L. Sandier, Guide to the French language; especially devised for persons who wish to study that language without the assistance of a teacher. the tenth edition, revised and corrected, London, page 70

In English there are four moods:–1. The Infinitive Mood. 2. The Indicative Mood. 3. the Imperative Mood. 4. The Subjunctive Mood.

1858, C. P. Mason, English grammar; including the principles of grammatical analysis, London, page 32

[…] to search out in some higher region of infinitive space a spot where it was impossible for defilement to follow them […]

a. 1823, Cunningham's Sermons (quoted in 1823, The Edinburgh Christian Instructor, volume 23, page 328)