Why does Dutch “zeemeermin” (mermaid) literally mean “sea-sea-maiden”?

Two kids at a pool say they’ve been playing zeemeermin, mermaid. The word is oddly doubled: meermin alone already meant “mermaid,” built from an older sense of meer as “sea” (not today’s “lake”) plus min, an old word whose origin is debated. Add zee (“sea”) to the front and “zeemeermin” says “sea” twice, once in each half of the word.

This kind of doubling is called a pleonasm, and “zeemeermin” has been documented in Dutch since at least 1623. Modern Dutch uses “meer” for “lake” (as in the IJsselmeer), so the old sea meaning hidden inside “meermin” is no longer obvious, and the “zee” at the front makes it clear again.