noun
ZoologyA bivalve mollusc of the family Unionidae; a unio.
adjective
ZoologyDesignating molluscs of the family Unionidae; relating to or characteristic of this family.
Origin
Mid 19th century; earliest use found in Philip Carpenter (1819–1877), social reformer and conchologist. From scientific Latin Unionidae, family name from Unio unio + -idae, with insertion of -n- after classical Latin ūniōn-, ūniō, etymon of the first element.
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