1. An instrument that measures and indicates the amount of x-rays or radiation absorbed in a given period: "During the patient’s treatment, the nurse carefully read and recorded the results of the therapy from the dosimeter."
2. A device carried by a person for measuring the quantity of ionizing radiation; such as, gamma rays, to which one has been exposed: "Part of the hospital experiment was to have the patients wearing a dosimeter for three weeks and then submitting to tests at the end of the period."