The one piece of figurative language that seems to rise above the rest in Robert Frost's poem, "The Road Not Taken," is symbolism.
Defined, symbolism is:
...when an object is meant to be representative of something or an idea greater than the object itself.
Though some people may see a contradiction, the "popular" understanding of the symbol of a path that comes to a fork in the woods is that the speaker has arrived at the point where he must make an important life-choice. His sense of individualism drives him to take the path that has been traveled more lightly so as not to follow the "common" path. Though the poem simply describes a walk in the woods, finding symbolism gives "The Road Not Taken" a much deeper meaning to an observant reader.
Personification is also used by Frost. He speaks of the path that "wanted wear." Personification occurs when human characteristics are given to non-human things. In this case, a path cannot "want" anything, but is personified by the author. Also, "having perhaps the better claim" may also be personification in saying that the path "deserved" or "asked" (referring to "claim") to be trodden upon because it had not been worn down.
Finally, we could say that "sigh" is an example of onomatopoeia, which is defined as...
...natural sounds [that] are imitated in the sounds of words (eg buzz, hiss)
In other words, it is when a word represents the sound that it stands for. The word "sigh" mimics the sound we make when we sigh.