What part of speech is tranquilize?

Tranquilize can be categorized as a verb.

Parts of speech

1. tranquilize is a verb, present, 1st person singular of tranquilize (infinitive).
2. tranquilize is a verb (infinitive).

Verb
tranquilize - make calm or still; "quiet the dragons of worry and fear"
tranquilize - cause to be calm or quiet as by administering a sedative to; "The patient must be sedated before the operation"