Diameter

wiktionary

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From Old French diametre (French diamètre), from Latin diametrus, from Ancient Greek διάμετρος(diámetros) ( γραμμή(grammḗ)) (diametros grammē, “line measuring across”), from διά(diá, “across”) + μέτρον(métron, “measure”).

etymonline

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diameter (n.)

late 14c., in geometry, "chord of a circle or sphere which passes through its center; the length of a diameter," from Old French diametre, from Latin diametrus, from Greek diametros (gramme) "diagonal of a circle," from dia "across, through" (see dia-) + metron "a measure" (from PIE root *me- (2) "to measure").