What part of speech is the word burnt?

The word "burnt" can be either a verb or an adjective, depending on how it's used in a sentence.

Verb:

* "I burnt the toast." Here, "burnt" describes the action of burning.

Adjective:

* "The burnt toast was inedible." Here, "burnt" describes the condition of the toast.

So, to determine the part of speech, look at its role in the sentence.