What part of speech is upchuck?

Upchuck can be categorized as a verb.

Parts of speech

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

Verb
upchuck - eject the contents of the stomach through the mouth; "After drinking too much, the students vomited"; "He purged continuously"; "The patient regurgitated the food we gave him last night"
Noun
upchuck - Vomit.