di ‧ am ‧ e ‧ ter /daɪˈæmətə, daɪˈæmɪtə $ -ər/ BrE AmE noun [countable]
[ Date: 1300-1400 ; Language: Old French ; Origin: diametre , from Greek diametros 'measure across' , from metron 'measure' ]
a straight line from one side of a circle to the other side, passing through the centre of the circle, or the length of this line
3 inches/1 metre etc in diameter
Draw a circle six centimetres in diameter.
diameter of
The diameter of the Earth is about 13,000 km.