A simile is a comparison between two unlike things, usually using the words "like" or "as."
1) "Life is like a box of chocolates. You never know what you're gonna get." - Forrest Gump
2) "A parson is like a doctor, my boy: he must face infection as a soldier must face bullets." - Candida by George Bernard Shaw
Unlike a simile, a metaphor states that an object or idea is in some way the same as another, seemingly unrelated thing. For example, where a speaker using a simile to insult someone might say, "He's like a rat," a speaker using a metaphor would say something like, "He's a real rat!" Of course, the person being insulted is not literally a rat; instead, the speaker is using a metaphor to draw a connection between his victim and a rather unsavory animal.
1) "That test was a total breeze." - Common expression
2) "You are my sunshine, my only sunshine. You make me happy when skies are gray." - Popular song
Personification, also known as "anthropomorphism," is the attribution of human qualities to non-human things. These can be objects, events, ideas, or even living, non-human things.
A few examples:
1) "The other houses of the street, conscious of decent lives within them, gazed at one another with brown imperturbable faces." - "Araby" by James Joyce
2) "Season of mists and mellow fruitfulness, / Close bosom-friend of the maturing sun; / Conspiring with him how to load and bless / With fruit the vines that round the thatch-eves run" - "To Autumn" by John Keats
Metonymy is an expressive style for describing something in an indirect way by usually referring to things associated with it.
Crown. (For the power of a king.)
The White House. (Referring to the American administration.
The Pentagon. (For the Department of Defense and the offices of the U.S. Armed Forces.)
Hollywood. (For US Cinema.)
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