An Etymological Dictionary of the German Language/Meer
Meer, n., ‘ocean, sea,’ from MidHG. męr, n., OHG. męri, earlier mari, m. and n., ‘ocean’; comp. OSax. męri, f., Du. meer, n., AS. męre, m., E. mere (to which merman, mermaid, are allied), OIc. marr, m., Goth. marei, f. (and *mar, n., preserved in the compound mari-saivs, ‘ocean’). The common Teut. word for ‘ocean,’ prim. Teut. mari, n. (or mori, recorded by Pliny as a Cimbrian form), which is partly common to the West Aryan tribes (so too Lat. lacus, OIr. loch, equiv. to OLG. lagu, ‘ocean’); Lat. mare, n., OSlov. morjc, n., ‘ocean,’ Lith. máres, ‘Kurisches Haff,’ OIr. muir (from mori), ‘ocean’; to these are allied Gr. Αμφίμαρος, ‘son of Poseidon,’ as well as ἀμάρα, f., ‘trench, conduit’ (comp. OFris. mar, ‘trench, pond’)?. These cognates are usually connected with the Aryan root mar, ‘to die’ (comp. Mord, Lat. morior), so that the ocean was named in “contrast to the living vegetation” of the mainland, just as in Ind. also marus, ‘desert,’ is referred to the root mar, ‘to die’; this, however, is no more probable than the derivation of Mann from the root men, ‘to think.’ Comp. Marsch and Moor.