The only free and comprehensive online etymological dictionary of the Spanish language
castellano (Adjective, Noun) "Castilian"
From Medieval Latin castellanus "(inhabitant) of Castile." See Castilla for a continued etymology.
Also the origin of towns named Castellanos in Burgos, Palencia, Valldolid, Leon, Zamora, Salamanca, Avila, Soria, Orense,and Pontevedra; all named between the 9th and 12th centuries.
Asturian castellanu
Castilla f. (Toponym) "Castile"
From Medieval Latin castella "forts," plural of Latin castellum (see castillo). On the reasoning for the name of the region, Roberts (2014) writes: "[S]o called from the many forts built by the Christians along the southern border of this region as a defense against the Moors."
Asturian castiella, Portuguese castela, Galician castela, Catalan castella, French Castille, Italian castella
castillo m. (Noun) "castle"
10th cent. From Latin castellum 'id.' From castrum "fort" (see castro (1)) and diminutive suffix -ellum (see -elo).
Castillo is behind the name of numerous toponyms. Also the origin of the surnames Castillo, del Castillo.
Asturian castiellu, Portuguese castelo, Galician castelo, Catalan castell, French château, Italian castello
Castillo y León. The united kingdoms of Castile and León, formally joined under the Crown of Castile in 1301. The kingdoms were primary actors in the Reconquista. Also the name for "heads or tails" / "cross or pile," as Medieval coins depicted a castle and a lion on each face.
castro (1) m. (Noun) "Roman fort;" (Galician) "Roman ruins," (Asturian) "pre-Roman ruins"
14th cent. From Latin castrum "fort." From Proto-Italic *kastro- "part." Developed in the sense of "the walled part (of a place)." From Proto-Indo-European *ḱs-tro- 'id.' From a root *ḱes- "to cut." Interestingly, in Proto-Indo-European there were two other roots meaning "to cut": *kers- and *sek- (cf. carmenar and señal).
Also the origin of the surname Castro.
Asturian castru, Portuguese castro, Galician castro, Romanian castru
Oscan castrous "of the estate," Umbrian castruo "field"
castro (2) m. (Noun) (Cantabria, Palencia, Zamora and León dialects) "hopscotch"
Called so because the lines resemble a castle's fortification. The game dates back to the Roman Empire.
causa f. (Noun) "cause"
13th cent. Borrowed from Latin causa 'id.' The natively inherited word in Spanish is cosa.
cayo m. (Noun) (especially regarding islands in the Antilles) "cay"
16th cent. Also attested are earlier forms cay, caic, caico. Borrowed from Antilles Taino cayo 'id.'
As a surname, found in Cayo, Caio, and San Cayo; also in Sephardic Callo.
-c, -ce Latin suffix indicating deixis, akin to "here" or "there."
Not productive in Spanish. From Proto-Italic *ke "here." From Proto-Indo-European *ḱe, meaning "this," "here."
Paelignian -c, Oscan -k, Marrucinian -c, Umbrian -c
Gothic hi- 'id.'
Lithuanian šìs 'id.,' Old Prussian schis 'id.,' Old Church Slavonic 'id.'
Ancient Greek -κε "this,"
cebolla f. (Noun) "onion"
13th cent. From Late Latin cepulla "little onion," diminutive of Latin cepa "onion," which survives in a smattering of surnames (see below). Of unknown origin. A potential cognate in Ancient Greek hints that the word was a loan.
Also the origin of the surnames Cebolla, Cebollo, and the conservative surnames Cebo, Cebe, Cebey, and Cebiel. probably given to onion farmers in older times.
Catalan ceba, French cive, Aromanian tseapã, Romanian ceapă
Ancient Greek καπια "onions"
Basque tipula "onion," (Bizkaian) kipula 'id.' (borrowed from Late Latin)
ceder (Verb) "to cede"
16th cent. Borrowed from Latin cedere "to yield," but originally "to proceed." From Proto-Italic *kesd-e/o- "to go away." From Proto-Indo-European *ḱi̯es-dh- "to drive away."
Sanskrit sedhati "to drive away," Old Avestan siiazdat̃