Simile is the comparison of two unlike things using like or as. Related to metaphor
He eats like a pig. Vines like golden prisons.
Poetry is, first of all, a communication - a thought or message conveyed by the writer to the reader. It is not only an act of creation, but an act of sharing. It is therefore important to the reader that he understands how the poet uses words, how he puts fresh vigor and new meaning into words. The reader's understanding is immeasurably increased if he is familiar with the many techniques or devices of poetry. Some of these are extremely simple; a few are rather elaborate.
The simplest and also the most effective poetic device is the use of comparison. It might almost be said that poetry is founded on two main means of comparing things: simile and metaphor. We heighten our ordinary speech by the continual use of such comparisons as "fresh as a daisy," "tough as leather," "comfortable as an old shoe," "it fits like the Paper on the wall," "gay as a lark," "happy as the day is long, pretty as a picture." These are all recognizable similes; they use the words "as" or "like."
A metaphor is another kind of comparison. It is actually a condensed simile, for it omits "as" or "like." A metaphor establishes a relationship at once; it leaves more to the imagination. It is a shortcut to the meaning; it sets two unlike things side by side and makes us see the likeness between them. When Robert Burns wrote "My love is like a red, red rose" he used a simile. When Robert Herrick wrote "You are a tulip" he used a metaphor. Emily Dickinson used comparison with great originality. She mixed similes and metaphors superbly in such poems as "A Book," "Indian Summer," and "A Cemetery." One of the Poems in her group ("A Book") illustrates another device -Of poetry: association - a connection of ideas. The first two lines of "A Book" compare poetry to a ship; the next two to a horse. But Emily Dickinson thought that the words "ship" and "horse" were too commonplace. The ship became a "frigate," a beautiful full-sailed vessel of romance; and the everyday "horse," the plodding beast of the field and puller of wagons, became instead a "courser," a swift and spirited steed, an adventurous creature whose hoofs beat out a brisk rhythm, "prancing" - like a page of inspired poetry.
Thus, because of comparison and association, familiar objects become strange and glamorous. It might be said that a Poet is a man who sees resemblances in all things.