Isotach

Part of speech: noun

Definitions

1. A line drawn on a weather map that connects all points where the wind blows at the same speed
2. A contour on a meteorological chart linking locations that share an identical wind velocity
3. An isoline showing places experiencing the same wind speed at a given time on a forecast map

Etymology: An isotach is a line on a weather map joining points where the wind speed is the same. Its name is built from two Greek-derived pieces: the prefix "iso-", meaning "equal", and "takhús", the Greek word for "fast", which also gave English the combining form "tachy-" (as in "tachycardia", a racing heartbeat). Put together, the name simply means "equal speed," and the word is a plain technical coinage made by meteorologists to describe a wind-speed contour, much as "isobar" joins points of equal pressure and "isotherm" joins points of equal temperature. The pattern is deliberate. Meteorology borrowed the "iso-" prefix from Greek to label lines of equal value, and attaching it to "tachy-" produced a term that reads at a glance as "same speed." Because the word is a compound of established classical elements rather than a traditional English word, its meaning has stayed fixed: it names only the wind-speed line and has not drifted into other senses.