Isocryme

Part of speech: noun

Definitions

1. A line drawn on a map linking all places that share the same average temperature during the coldest part of the year
2. A contour on a climate chart connecting locations whose mean winter temperatures are equal
3. The curved boundary on a weather map that marks areas with identical average cold-season temperatures

Etymology: James D. Dana, the American geologist and naturalist who served on the United States Exploring Expedition, coined "isocryme" in 1854, though the word first appeared in print in his 1852 paper on the geographical distribution of crustaceans. He needed a term for the lines on a map that join places sharing the same average temperature during the coldest part of the year, and he built it from two parts. The first is the Greek prefix "iso-", meaning "equal", which appears in many scientific coinages. The second comes from Greek "krumos", meaning "cold" or "chilliness", a relative of "kruos", "frost". Dana's choice reflects the scientific habit of the mid-nineteenth century, when naturalists turned to classical Greek to name new concepts. The word therefore has no ancient history at all: the Greeks had the root for cold, but they never combined it with "iso-" to describe a temperature line. "Isocryme" belongs to the same family as "isotherm", and it names a single, specialised idea rather than a word that drifted through everyday speech.