It can be used as either an adjective or noun. As an adjective it can me suitable/ appropriate or practical/ convenient. As a noun it means a mean of attaining an end. However this would be attained by a way that is convenient but considered improper.
Using a dictionary is the most expedient way to learn the meaning of new words if one is right in front of you.
The elevator was a useful expedient for getting to the tenth floor.
Hope this helped!