What part of speech is lambaste?

Lambaste can be categorized as a verb.

Parts of speech

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

Verb
lambaste - censure severely or angrily; "The mother scolded the child for entering a stranger's car"; "The deputy ragged the Prime Minister"; "The customer dressed down the waiter for bringing cold soup"
lambaste - beat with a cane