Definition of: infinitive

(in·fin′ə·tiv) Gram. adjective
1. Without limitation of person or number: opposed to finite.
2. Of, pertaining to, or using the infinitive mood.
—noun In many languages, a mood of the verb expressing action or condition without the limitation of person or number, as to run. In English, its sign to is omitted after the auxiliaries can, could, do, may, might, must, shall, should, will, would, and after such phrases as had better, had rather, and is used optionally after bid, dare, help, let, make, need, please, see, etc. The infinitive may also function as a noun while retaining the ability of the verb to take objects and adverbial modifiers. Example: To ride horses was his favorite sport. Also infinitive mood.
—split infinitive An expression in which the sign of the infinitive “to” is separated from its verb by an intervening word, usually an adverb, as in the phrase “to quickly return.” Although the construction is often condemned, it is sometimes justified to escape ambiguity. [<LL infinitivus]