late Middle English: from Old French diametre, via Latin from Greek diametros (grammē) ‘(line) measuring across’, from dia ‘across’ + metron ‘measure’
中世後期英語:古フランス語のdiametreから、ラテン語のdiametros (grammē) '(line) measuring across', from dia 'across' + metron 'measure' を経て、ギリシャ語。