The only free and comprehensive online etymological dictionary of the Spanish language
naturaleza f. (Noun) "nature"
Early 13th cent. From natural and -eza, an abstract noun-forming suffix.
nave f. (Noun) "ship"
In 10th cent. derivation naveta. First direct attestation is 12th cent. From Latin navis 'id.' From Proto-Italic *nāw- 'id.' From Proto-Indo-European *neh2-u̯- 'id.' From the root *neh2- "to swim" (see nadar).
Indo-European
Romance
Asturian nave, Portuguese nave, Galician nave, Catalan nau, French nef, Italian nave, Aromanian nai, Romanian naie, Sardinian nae
Celtic
Old Irish náu "ship," Middle Welsh noe "bowl," Middle Breton neau "vase"
Germanic
Old Norse nór "ship," Norwegian no "wooden bowl," Old English nōwend "skipper"
Hellenic
Ancient Greek ναῦς (naûs) "ship"
Armenian
Armenian naw "boat"
Indo-Iranian
Sanskrit náu- "ship," Young Avestan nāuu(a)iia- "crossable by ship"
navidad f. (Noun) "Christmas"
Early 13th cent. Old Spanish nadvidad, from natividad. From Latin nativus "born," from nascor "to be born" (see nacer) and -ivus (see -ivo).
Indo-European
Romance
French naïf, natif, Italian nativo, Romanian nativ
necesario (Adjective) "necessary"
13th cent. From Latin necessarius 'id.,' formed from necesse "necessary" and -arius, an adjective-forming suffix (see -ario). Necesse derives from ne- "not" and cesse "avoiding." Hypothetically, cesse is from *ced-tis "avoidable," with the first element is from the verb cedere "to withdraw" (see ceder). While every linguist connects cesse with cedere in some way, the precise path the word took is unclear (see de Vann (2014) for further discussion).
Indo-European
Romance
French nécessaire, Italian necessario
necesitar (Verb) "to need;" "to necessitate"
17th cent. From Medieval Latin necessitare 'id.,' a verb formed from Latin necessitas "necessity," from necesse "necessary" (see necesario for further etymology of necesse) and -itas, a noun-forming suffix indicating a state of being (see -edad).
Nesitar, colloquial in Aragon and Latin America, probably dates back to a Medieval haplology.
Indo-European
Romance
French nécessité, Italian necessità
negociar (Verb) "to negotiate"
Late 15th cent. From Latin negotiare 'id.' From negotium "business" (see negocio).
Indo-European
Romance
Portuguese negociar, Catalan negociar, French négocier, Italian negoziare, Romanian neguța
negocio m. (Noun) "business"
13th cent. From Latin negotium 'id.,' a compound of nec "not" (see ni) and otium "leisure" (see ocio).
Indo-European
Romance
Asturian negociu, Portuguese negócio, Catalan negoci, French négoce, Italian negozio, Romanian negoț
"The Latin negōtium... has a peculiar history:

"A calque on Gr. a-skholía, neg-ōtium conveys the same senses as the Greek model, which are positive despite the negative formation: “occupation, impediment, difficulty.”

"At a later stage negōtium is the equivalent of Gr. prâgma ‘a thing’, but also more specifically and especially in derivations “commercial affairs.” A calque, semantically this time, on prâgma , negōtium becomes the designation for “business.”" ~ E. Benveniste, Indo-European Language and Society (1973)
negro (1) (Noun) "black (person)"
From Latin nigrum, accusative of niger "black (person)" but the sense of niger as an abstract color is first (see negro (2)).
As a surname, it follows a tradition dating to Roman times; given to people black or dark of skin.
Indo-European
Romance
Asturian negru, Portuguese negro, Galician negro, Catalan negre, French nègre, Italian negro, Aromanian negru, Romanian negru, Sardinian négru
negro (2) (Adjective, Noun) "black"
12th cent. From Latin nigrum, accusative of niger 'id.' Of unknown origin. Possibly related to Tocharian B ñakre "darkness." If so, an ancestral word *ni̯g(h)-ro- or *ni̯ǵ(h)-ro- 'id.' is reconstructed in Proto-Indo-European by Isebaert (1977).
As a surname, it was given to people with black hair or beards, but see also negro (1).
Indo-European
Romance
Asturian negru, Portuguese negro, Galician negro, Catalan negre, French nègre, Italian negro, Aromanian negru, Romanian negru, Sardinian négru
Némesis f. (Noun) Goddess of retribution.
From Latin Nemesis 'id.' Taken from the Ancient Greek Νέμεσις (Némesis) 'id.,' which as a name comes from the verb νέμω (némo) "I distribute." From Proto-Indo-European *nem- "to distribute" (of the same origin as número).
Indo-European
Germanic
Gothic niman "to take," Old Norse nema 'id.,' Old High German neman 'id.,' Old English niman 'id.' (English nim)
Balto-Slavic
Latvian nemt "take"