From Middle English mereman, from Old English *meremann (“merman") (suggested by Old English meremenn, meremennen, meremenin (“mermaid, siren"), equivalent to mer- +"Ž man. Cognate with Dutchmeerman (“merman"), GermanMeermann (“merman").
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The name Dagon seems to come from ddg " fish," and that his idol was half-man half-fish is possible from the ichthyomorphic representations found upon coins of Ascalon and Arvad, and from the fact that Berossus speaks of an Assyrian merman-god.