To become larger or wider, or to make something larger or wider.
From Latin 'dilatare,' combining 'di-' (meaning 'apart') with 'latus' (meaning 'wide'). The literal meaning of 'spreading wide' evolved into the modern sense of expanding or enlarging.
Your pupils dilate (get bigger) automatically in dim light to let in more light, and they constrict (get smaller) in bright light—this is why doctors shine a light in your eyes to check if your reflexes are working! Emotions can also cause dilation: pupils dilate when you see something you find attractive.
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