Achondrite

Part of speech: noun

Definitions

1. A classification of stony meteorites that are characterized by an absence of chondrules, typically composed of various silicate minerals
2. A specific group of meteorites that do not contain chondrules and are mainly formed from silicate materials
3. A type of stony meteorite distinguished by the lack of small spherical grains called chondrules and composed predominantly of silicate minerals

Etymology: The most surprising thing about "achondrite" is that its first half is a negation borrowed from Greek and its second half is a mineral-science coinage, so the word describes a rock by what it lacks. "Chondrite" comes from Greek "chondros," meaning grain, and refers to the tiny round grains that are embedded in many stony meteorites. The prefix "a-" is the Ancient Greek privative, meaning "without" or "not," the same element found in words like "atheist" or "anaemia." Put together, an achondrite is a stony meteorite that has no chondrules. The compound is a modern scientific formation, not an ancient one. Ancient Greeks had no word for meteorites in this sense, and the terms were built in English from classical elements to classify the rocks once they were studied as a group. The pattern is simply prefix plus existing term, the same way scientists have long named things by what they are not.