B1
a unit of length which is equal to 0.001 meters
Dictionary examples:
My pencil is now only one millimeter long. Time for a new one! (0.0)
My new diet helped me lose a whole millimeter off my waist! (0.0)
I moved my desk a millimeter to the left. The room looks so different! (0.0)
The ring has a width of three millimeters. (33.6)