The only free and comprehensive online etymological dictionary of the Spanish language
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.

Romance: Western Vulgar Latin: Asturian mar, Portuguese mar, Galician mar, Catalan mar, French mer, Italian mare; Eastern Vulgar Latin:amari, Romanian mare; Sardinian:mare

Indo-European: 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, cf. mermaid); Balto-Slavic: Old Church Slavonic morje "sea," Russian móre 'id.,' Czech moře 'id.,' Slovene morję̑, 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).
maravilla f. (Noun) "wonder"

12th cent. From Latin marabilia 'id.,' from mirabilis "wonderful," from mirari "to look (at)" (see mirar).

Romance: Western Vulgar Latin: Portuguese maravilha, Catalan meravella, French merveille, Italian meraviglia
maravilloso (Adjective) "marvelous," "awesome"

12th cent. From maravilla.
marca f. (Noun) "mark;" "brand"

Very late 15th cent. Borrowed from Gothic *marka- "mark." From Proto-Germanic *marka- "sign." From Proto-Indo-European *morg-o- 'id.'

Romance: Western Vulgar Latin: French marc, Italian marca

Germanic: North Germanic: Old Norse mark "sign;" West Germanic: Middle Dutch marc "trademark," Old English meark "mark" (English mark)
marcha f. (Noun) "movement;" "departure"

17th cent. From marchar.
marchar (Verb) "to walk;" "to depart"

16th cent. Borrowed from Old French marcher "to march," itself borrowed from a Germanic source meaning to mark a boundary by footstep. From Proto-Germanic *markō- "boundary." From Proto-Indo-European *morǵ- 'id.'

Italic: Latin margo "edge"

Germanic: East Germanic: Gothic marka "boundary;" North Germanic: Old Norse mǫrk "forest;" West Germanic: Old High German marka "border," Old Saxon marka 'id.,' Old English mearc 'id.'

Indo-European: Celtic: Gaulish brogae "territories," Old Irish mruig "territory," Middle Welsh bro 'id.,' Old Breton bro 'id.,' Cornish bro 'id.;' Indo-Iranian: Young Avestan marəza- "border;" Anatolian: Hittite mārk-i "to divide"
María (1) f. (Noun) "Mary"

From Latin Maria, borrowed from Hebrew Miryām, a name meaning "well-nourished one" (Knaupf 2011).

Today popular in first and last names, as well as variants Mari, Marías, Santamaria, Santa María and Mariátegui (from Basque meaning "house of Mary").
maría (2) f. (Noun) (pejorative) "maid"

From the name María (1), arising as a stereotype of the personal names of domestic workers.
maría (3) f. (Noun) "Spanish silver coin"

Originally referring to a talero de María Teresa "Mary Theresa thaler," a famous Vienna coin used the world over. Mary Theresa, whose face adorned the thaler, was the first and only Holy Roman Empress.
marido m. (Noun) "husband"

11th cent. From Latin maritus "marital," from mas "male," a word preserved in Eastern Romance languages (Romanian mare "great"). From Proto-Italic *mās- 'id.' From Proto-Indo-European *meh2-s 'id.'

Romance: Western Vulgar Latin: Asturian maríu, Portuguese marido, Catalan marit, French mari, Italian marito; Eastern Vulgar Latin: Aromanian mãrit, Romanian mărit; Sardinian: maridu

"To begin with, we find the words for “husband” and for “wife,” which we will consider in their Latin expressions, marītus and uxor.

"Marītus is peculiar to Latin: as a matter of fact, there is no Indo-European word signifying “husband.” Sometimes the expression “master” was used, e.g. Skt. pati, Greek pósis (πόσις), without any special indication of the tie of conjugality; sometimes we find “the man,” Lat. vir, Gr. anḗr (ἀνήρ), whereas marītus designated the husband in his legal aspect." ~ E. Benveniste, Indo-European Language and Society (1973)