: a straight line that runs from one side of a figure and passes through the center Measure the diameter of the circle. 2 : the distance through the center of an object from one side to the other : thickness the diameter of a tree trunk. diameter.
: a straight line that runs from one side of a figure and passes through the center Measure the diameter of the circle. 2 : the distance through the center of an object from one side to the other : thickness the diameter of a tree trunk. diameter.