What part of speech is the word trouble?

The word "trouble" can be several parts of speech, depending on how it's used in a sentence:

* Noun: "I'm in trouble." (Refers to a difficult situation)

* Verb: "Don't trouble yourself with this." (Means to cause difficulty or annoyance)

* Adjective: "The troubled waters of the bay." (Describes something difficult or causing worry)

So, to determine the part of speech for "trouble", you need to look at its context in the sentence.