word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (source also of Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian prie "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "forward," hence "beyond, in front of, before."
The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.
1650s, "from or of Wales or the Welsh," from Cambria, variant of Cumbria, Latinized derivation of Cymry, the name of the Welsh for themselves, from Old Celtic Combroges "compatriots." Geological sense (in reference to Paleozoic rocks first studied in Wales and Cumberland) is from 1836.
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<a href="https://www.etymonline.com/word/precambrian">Etymology of precambrian by etymonline</a>
Harper, D. (n.d.). Etymology of precambrian. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/precambrian