The Collaborative International Dictionary of English v.0.48:

Oxide \Ox"ide\ ([o^]ks"[i^]d or [o^]ks"[imac]d), n. [F.
   oxyg[`e]ne oxygen + acide acid: cf. F. oxyde. The French word
   was correctly spelt oxide, till about the year 1840, when, in
   ignorance or forgetfulness of the true history and
   composition of the word, the orthography was change to make
   it represent the [upsilon] of Gr. 'oxy`s, from which it was
   supposed to be directly derived.] (Chem.)
   A binary compound of oxygen with an atom or radical, or a
   compound which is regarded as binary; as, iron oxide, ethyl
   oxide, nitrogen oxide, etc.
   [1913 Webster]

   Note: In the chemical nomenclature adopted by Guyton de
         Morveau, Lavoisier, and their associates, the term
         oxides was made to include all compounds of oxygen
         which had no acid (F. acide) properties, as contrasted
         with the acids, all of which were at that time supposed
         to contain oxygen. The orthography oxyde, oxyd,
         etc., was afterwards introduced in ignorance or
         disregard of the true etymology, but these forms are
         now obsolete in English. The spelling oxid is not
         common.
         [1913 Webster] oxidise