Antithesis is a figure of speech that places contrasting ideas, images, or words side by side for emphasis. The contrast is usually balanced and deliberate, so the two parts sharpen each other: light against dark, hope against despair, peace against war. Poets use antithesis to create tension, highlight a choice, or make a thought feel more forceful and memorable.
Example
She moved with summer in her step,
I carried winter in my hands.
Her voice said stay; my silence said go.
[n] the juxtaposition of contrasting words or ideas to give a feeling of balance
[n] exact opposite; "his theory is the antithesis of mine"