köldur

Köldur is the Icelandic adjective meaning cold. It describes low temperatures in weather, on objects, and more broadly in contexts where heat is lacking or perceived as weak. The word is used in everyday speech to refer to both physical temperature and figurative states, such as a cold reception or a cold environment.

In physics, cold refers to states with low thermal energy. Temperature is the measure of this energy, and common scales for everyday use are Celsius and, in scientific contexts, Kelvin. Absolute zero, the theoretical limit where particle motion ceases, is 0 kelvin (−273.15 degrees Celsius). Water freezes at 0 °C, and many substances change their properties as temperature decreases.

For everyday life, cold is perceived relative to the observer and conditions such as wind and humidity. Weather forecasts typically report air temperature in Celsius in Iceland and much of Europe, while wind chill can make the air feel colder than the measured temperature. Thermometers are used to quantify cold, and clothing, shelter, and heating practices are designed to cope with low temperatures.

Effects of cold extend to biology and engineering. Low temperatures slow chemical reactions, influence biological processes, and can cause frostbite or hypothermia if exposure is prolonged. Materials may contract or become brittle when cooled, while some processes and storage conditions require refrigeration to preserve quality.

Etymology traces Köldur to the Icelandic language family and its historical development within Nordic languages, reflecting the broad concept of absence or reduction of heat that is central to the term.