in·fin·i·tive 
(ĭn-fĭnĭ-tĭv)
(ĭn-fĭnĭ-tĭv)n. Abbr. inf. or infin.
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. See Usage Note at split infinitive.
[From Middle English infinitif, of an infinitive, from Old French, from Late Latin īnfīnītīvus, unlimited, indefinite, infinitive, from Latin īnfīnītus, infinite; see INFINITE.]