/
dʌɪˈamɪtə/
n.
  - a straight line passing from side to side through the centre of a body or figure, especially a circle or sphere. 
▸a transverse measurement of something; width or thickness.
 - a unit of linear measurement of magnifying power.
 
Derivative
Etymology
ME: from OFr. diametre, via L. from Gk diametros (grammē) ‘(line) measuring across’.