The only free and comprehensive online etymological dictionary of the Spanish language
zacate f. (Noun) (Latin America) "grass"

16th cent. Borrowed from Nahuatl zacatl 'id.'

Found as a surname in Zacate, in the conservative form Zácatl, and with honorific suffixes in Zacatzi and Zacateco. Also found in the surname Zacatenco "on the grassy coast," from Nahuatl zaca (apocopation of zacatl) and ten "coast."
zaga f. (Noun) rear

12th cent. From Andalusian Arabic sáqa 'id.' From Arabic sāqah "rearguard."
zanahoria f. (Noun) "carrot"

14th cent. Old Spanish çanahoria, dialectic variant safanòria. Borrowed from Andalusian Arabic *safunnárya 'id.,' itself borrowed from Ancient Greek σταφυλίνη ἀγρία (staphulíne agría) "wild carrot." Σταφυλίνη "carrot" is a diminutive of σταφυλή (staphulé) "grape," of unknown origin. Ἀγρία, when referring to plants meaning "wild," is from ἀγρός (agrós) "field" (see agro).

Romance: Western Vulgar Latin: Catalan (Mallorca) safanària
zapato m. (Noun) "shoe"

10th cent. Old Spanish çapato. Of unknown origin but it must be a borrowing from another language. The voicing to <z> in Spanish is unexpected but not without precedent; it sporadically occurs in Old Portuguese documents as well. In Iberian and Italian, the meaning is of shoes, but in Gallo-Romance the sense is pejorative.

Romance: Western Vulgar Latin: Portuguese sapato, Italian ciabatta

"Una palabra semejante existe en las lenguas eslavas del Norte ..., en turco septentrional ..., y alguna forma semejante se ha empleada en persa, pero no es seguro que haya relación etimológica entre estas palabras orientales y las lenguas de Occidente; si hubo propagación de las unas a las otras, no consta el lugar de origen; la documentación más antigua que hasta ahora se ha encontrado procede de España cristiana y de la parte musulmana del mismo país, y en ninguna parte se encuentra una etimología que se imponga por razones lingüísticas." ~ J. Corominas, Diccionario crítico etimológico castellano e hispánico, (1991).
zarpar (Verb) to drop anchor; "to set sail"

Very early 17th cent. From Old Italian sarpare 'id.,' from serpe "place in the prow to keep an anchor," "serpent," so-called for the space's snake-like appearance. From Vulgar Latin serpes "serpent" (see sierpe).
zona f. (Noun) "zone"

15th cent. From Latin zona "belt," "zone;" borrowed from Ancient Greek ζώνη ‎(zdóne) "belt," "zone." The meaning of belt is original. From Proto-Indo-European *i̯eh3s-neh2 "girdle." From the root *i̯eh3s- "to gird."

Romance: Western Vulgar Latin: Galician zona, Catalan zona, French zone, Italian zona; Eastern Vulgar Latin: Romanian zonă