IPA: /ˌɪn.fɪˈnɪt.ɪ.vəl/
KK: /ɪnˈfɪnɪtɪvəl/
Connected to the basic form of a verb that usually expresses an action or state without indicating tense.
The infinitival form of the verb is often used to express purpose.
Infinitival is formed from "infinitus" (from Latin, meaning unbounded or unlimited) and the suffix "-al" (meaning relating to). The term refers to something that relates to the infinitive form of a verb, which is often considered unbounded in terms of tense or subject.
Think of 'unbounded' ('infinitus') to remember that 'infinitival' relates to the unlimited form of a verb.