di·la·tion \dīˈlāshən, də̇ˈ-, ÷ˌdīəˈl-\noun (-s) Etymology:dilate (I) + -ion 1.: the act of dilating or the state of being dilated : expansion, dilatation 2.: the action of stretching or enlarging an organ or part of the body < dilation of the cervix > < dilation of the pupil by atropine >