Noun:
* "She gave him a look of disapproval." Here, "look" refers to an expression on her face.
* "The detective was on the lookout for clues." Here, "lookout" is a noun phrase meaning a position of observation.
Verb:
* "Look at the beautiful sunset!" Here, "look" means to direct your eyes towards something.
* "He looked tired." Here, "looked" is the past tense of the verb "look," meaning to appear or seem.
Adjective:
* "This is a look-alike of the original painting." Here, "look-alike" is a compound adjective meaning similar in appearance.
So, it's important to consider the sentence to determine the part of speech.