Omega, like eta, discussed elsewhere in this atlas, entered the Greek alphabet used today through the Ionic script reform Athens adopted by decree in 403 BCE, under the archon Eucleides; the older Athenian local alphabet had no separate sign for a long o sound and wrote it the same way as short o, using omicron, but the Ionic alphabet had already split the vowel into omicron for short o and a new letter, omega, meaning great o, for the long one. Omega's ancient meaning as the alphabet's last letter, and its Christian pairing with alpha discussed elsewhere in this atlas, is well known; its modern technical uses are more scattered.
Physicists use lowercase omega for angular velocity and for angular frequency in wave equations, and the SI unit of electrical resistance, the ohm, is written with an uppercase Omega, chosen in the 19th century in honour of the physicist Georg Ohm and, incidentally, for the letter's resemblance to a horseshoe-shaped resistor coil. Omega-3 and omega-6 fatty acids, common in nutrition science, take their names instead from a chemical convention that counts carbon atoms from the far end of a molecule's chain, the end chemists label omega by analogy with the letter's position as the alphabet's last.