rectal thermometer

a clinical thermometer that is inserted in the rectum.
Found on http://www.encyclo.co.uk/local/21001

Rectal Thermometer

A thermometer that is used to take a temperature in the rectum. Obtaining a temperature reading in the rectum is the most accurate method for diagnosing a fever. When taking a rectal temperature, it is recommended to use a water-based lubricant to ease any discomfort.
Found on http://www.pregnology.com/AZ/R/1
No exact match found