An Etymological Dictionary of Astronomy and Astrophysics

Any chord passing through the center of a figure. The length of this chord.

Etymology (EN): O.Fr. diamètre, from L. diametrus, from Gk. diametros “diagonal of a circle,” from dia- “across, through” + metron “a measure” → meter.

Etymology (PE): Tarâmun, from tarâ- “across, through,” → trans-

• mun/mân “measure,” as in Pers. terms pirâmun “perimeter,” âzmun “test, trial,”
  peymân “measuring, agreement,” peymâné “a measure; a cup, bowl,”
  from O.Pers./Av. mā(y)- “to measure,” cf. Skt. mati “measures,” matra- “measure,” Gk. metron “measure,” L. metrum; PIE base *me- “to measure.”