1. A unit of length equal to one thousandth of a metre, or approximately 0.039 inches.
Usage: British spelling; American English uses 'millimeter'; Commonly abbreviated as 'mm'

Examples

• The thickness of the paper is about 0.1 millimetres.
• A millimetre is a very small unit of measurement used in engineering and medicine.
• The ruler shows measurements in both centimetres and millimetres.
• The gap between the two parts must be precise to within a millimetre.
• Modern smartphones are often less than 10 millimetres thick.