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before vowels phren-, word-forming element meaning "mind," also "diaphragm," from Greek phreno-, comb. form of phrene properly "diaphragm, muscle which parts the abdomen from the thorax;" in Homer extended to "parts around the heart, breast," hence "heart" (as a seat of passions), "mind, seat of thoughts, wits, senses," of unknown origin.
phreno- or phren- or phreni-