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mar m. & f. (Noun) "sea"
12th cent. From Latin mare 'id.' From Proto-Italic *mari- "sea." From Proto-Indo-European *mor-i̯- "sea," but also "lake."
Typically masculine except in poetry, among seafarers, and in other limited environments. The feminine form is a secondary development, however. The word is the origin of the surnames Mares, del Mar, de la Mar, and Delmares.
Indo-European
Romance
Asturian mar, Portuguese mar, Galician mar, Catalan mar, French mer, Italian mare, amari, Romanian mare, Sardinianmare
Celtic
Gaulish Mori-ni (name) "(people) of the sea," Old Irish muir "sea," Welsh mor 'id.,' Old Breton mor 'id.,' Old Cornish mor 'id.'
Germanic
Gothic mari-saihws "sea," Old Norse marr 'id.,' Old High German mari 'id.,' Old English mere 'id.,' (English mer, first element in mermaid)
Balto-Slavic
Old Church Slavonic morje "sea," Russian móre 'id.,' Czech moře 'id.,' Slovene morję̑ 'id.,' Old Prussian mary 'id.,' Lithuanian mãrės 'id.'
Indo-Iranian
Ossetic mal "stagnant water"

La mar de tonto "Absolutely stupid." From the use of the feminine as a colloquial intensifier (Butt & Benjamin 2004).