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quadrilateral (n.)

"four-sided," 1640s, with -al (1) + Latin quadrilaterus, from quadri- "four" (from PIE root *kwetwer- "four") + latus (genitive lateris) "the side, flank of humans or animals, lateral surface," a word of uncertain origin. As an adjective from 1650s. Related: Quadrilaterally.