Unionidae unionid • unioniform · · · Info · Definitions · Characters · · Unionidae · · Text Latin · · Script 9 · · Length Definitions · · · (noun) freshwater mussels found worldwide. Synonyms: family Unionidae. · · Noun Definition 1 Characters · · U latin capital letter u U+0055 a latin small letter a U+0061 d latin small letter d U+0064 e latin small letter e U+0065 i latin small letter i U+0069 n latin small letter n U+006E o latin small letter o U+006F