Phrase for poetically skipping a word because it's been previously said

A professor of mine once used a phrase or term for skipping a word of a poetic statement that has already been said. His example was that "a stitch in time saves nine" should really be "a stitch in time saves nine stitches", but since you already know the subject of the sentence, it can just be skipped over.

Does anyone know a phrase to describe that?