The only free and comprehensive online etymological dictionary of the Spanish language
nada f. (Noun) "nothing"
11th cent. From Vulgar Latin nata "nothing," "little thing." Note an Old Spanish phrase cosa nada "little thing" (10th cent.). From the Latin phrase res nata "the question at hand" (but more literally, "the thing born"). For further etymology of nata, see nacer.

Note that Spanish de nada to answer to gratitude is mirrored in Catalan de res "you're welcome."