Definition - The omission of letters or syllables for the sake of poetic meter.

Example -

Roses are red, violets are blue
Money is green'n I've got none too.

Etymology -
The word derives from the Greek ek, out + thlibein, to squeeze or press.

Oxford English Dictionary -
Its first citation is from 1657: "Ecthlipsis … a striking out. It is a figure of Prosodia, especially when (M) with his vowel is taken away, the next word beginning with a vowel."
(J. Smith Myst. Rhet. 175 )

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