• diachronic •
Pronunciation: dai-ê-krah-nik • Hear it!
Part of Speech: Adjective
Meaning: Historical, related to changes occurring over time.
Notes: This word is probably used more frequently in linguistics, the science of language, than elsewhere. Its antonym is synchronic "the study of a subject in a current state, without regard for its history". Synchronic linguistics is the study of languages as they stand today. The adverb is, as expected, diachronically, and the noun, diachrony.
In Play: I am familiar with uses of today's word in linguistics. 'Diachronic linguistics' is the study of the changes in language, like the Word History of each Good Word. Etymology is the diachronic study of words. However, historical linguistics is not the only subject that may be described as "diachronic": "I prefer historical novels that are structured according to theme rather than those that are diachronic."
Word History: Today's Good Word was created around the mid-19th century out of Greek pieces: dia "through" + chronos "time" + ic-, an English adjective suffix corresponding to the Greek adjectival suffix -ik. Dia is presumed to be a combination of duo "two" + -a, an unknown suffix. It may be related to dis "twice". It occurs in a multitude of English borrowings from Greek, diametric, diatribe, diagram, to mention only a few. Chronos is another mysterious Greek word that occurs in many English borrowings: chronic, chronology, and synchronic, comprising syn "with" + chronos + -ic. There are no known sources of either of these two Greek words. (Now we must thank George Kovac, who suggested synchronically today's very Good Word.)