Dickinson also employs irony, created when what we expect to happen differs significantly, or is even opposite, of what actually occurs in reality. In this poem, the speaker claims that it is really the loser, the person who never wins or succeeds, who more fully understands what it means to achieve success or triumph. The speaker says,

Not one of all the purple host
Who took the flag to-day
Can tell the definition,
So clear, of victory! (lines 5-8)

In other words, no one can define victory as well as the person who has desired it but has never actually experienced it firsthand. The loser, then, actually comprehends what it means to win even better than the winner. Such a claim is probably the opposite of what most people would expect. After all, how could a person who has never succeeded possibly understand success better than someone who has actually experienced it? Dickinson seems to argue that the "defeated," who seems to have been "forbidden" a taste of triumph, is most capable of recognizing it.

In the final lines of the poem, Dickinson also uses a metaphor to compare the feeling of "triumph" to a song when she refers to its "distant strains" that may or may not reach one’s "ear."

There are several techniques in the poem.  The first is rhyming The words that rhyme in her poem are "succeed/need", and "ear/clear".  She also uses imagery in the last stanza (imagery is using the 5 senses to describe something).  She describes, "On whose forbidden ear/the distant strains of triumph/Break, agonized and clear."  She is describing the sounds of triumph very descriptively, which is imagery.  She also describes the army as a "purple Host", an image that fits with imagery.

Then, for figurative language techniques, there is a metaphor.  She compares people who appreciate success the most to someone who appreciates nectar because they are starving.  She says, "To comprehend a nectar/requires sorest need."  This enhances the point that she is making, that success often is counted the sweetest to those who have fought and struggled for it, and never tasted it.

I hope that helps!