or de·gree day


noun Engineering.

one degree of departure, on a single day, of the daily mean temperature from a given standard temperature. Abbreviation: dd

Nearby words

  1. degree,
  2. degree day,
  3. degree of curve,
  4. degree of difficulty,
  5. degree of freedom,
  6. degression,
  7. degressive,
  8. degressively,
  9. degu,
  10. degum

Origin of degree-day

First recorded in 1925–1930 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for degree day

degree day


a day on which university degrees are conferred



a unit used in estimating fuel requirements in heating buildings. It is equal to a fall of temperature of 1 degree below the mean outside temperature (usually taken as 18°C) for one day
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Science definitions for degree day


A unit of measurement equal to a difference of one degree between the mean outdoor temperature on a certain day and a reference temperature. The unit is most often used in estimating the energy needs for heating or cooling a building (for example, heating degree-days and cooling degree-days). Originally, degree-days were used to determine the relationship between temperature and plant growth. The term continues to be used in life sciences as a measure of upper- and lower-temperature limits for organisms.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.