móri
“body of water, sea, lake”sea, waters
PIE noun root for a body of water, sea, or lake. Source of Latin mare, English "mere," and words for large bodies of water.
Discussion
*móri is a Proto-Indo-European noun root meaning "body of water," "sea," or "lake"—one of the fundamental hydrological terms of the proto-language.
Latin mare "sea" is the best-known reflex, yielding English marine, maritime, mariner, and marsh (from *mori-sko-). Old English mere "lake, pool, sea" (modern English mere, as in a small lake) preserves the Germanic reflex, as do German Meer "sea" and Dutch meer "lake." Old Irish muir "sea" continues the Celtic form.
Slavic morje "sea" (Russian more, Polish morze) and Lithuanian marės "lagoon" confirm Balto-Slavic attestation. The wide distribution across all major branches makes this one of the most securely reconstructed PIE nouns.
The original meaning was likely "standing body of water" in general, with specialization to "sea" occurring in coastal-dwelling daughter cultures (Latin, Celtic, Slavic) while inland groups retained the "lake" sense (Germanic mere). This semantic variation has been used in homeland debates.
Modern descendants include English marine, maritime, marsh, mere, mermaid ("sea-maid"), and the proper name Moray.
Notes
Source of Latin "mare" (sea), English "mere", "marine". Core maritime term.