Definition of diameter noun from the Oxford Advanced Learner's Dictionary



    BrE BrE//daɪˈæmɪtə(r)//
    ; NAmE NAmE//daɪˈæmɪtər//
    Mathematical terminology
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  1. 1a straight line going from one side of a circle or any other round object to the other side, passing through the centre the diameter of a tree trunk The dome is 42.3 metres in diameter. compare radius See related entries: Mathematical terminology
  2. 2(specialist) a measurement of the power of an instrument to magnify something a lens magnifying 300 diameters (= making something look 300 times larger than it really is)
  3. Word Originlate Middle English: from Old French diametre, via Latin from Greek diametros (grammē) ‘(line) measuring across’, from dia ‘across’ + metron ‘measure’.Extra examples The mirror is 25cm in diameter. The tubes have an internal diameter of 2 mm. a method of calculating the diameter of the earth The diameter of the tree trunk was more than a metre. The dome is 42.3 metres in diameter. The radius of a circle is half its diameter.
See the Oxford Advanced American Dictionary entry: diameter