THREADFIN Meaning of THREADFIN in English ˈ ̷ ̷ˌ ̷ ̷ nounEtymology: so called from the filaments of the pectoral fin1. : a fish of the family Polynemidae2. : a fish of the genus Polymixia Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012