What part of speech is interline?

Interline can be categorized as a verb.

Parts of speech

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

Adjective
interline - Between or with two airlines.
Verb
interline - To write or insert between lines already written or printed, as for correction or addition.
interline - To arrange in alternate lines.
interline - To mark or imprint with lines.