Definition of protoxide in US English:

protoxide

noun

Chemistry
rare
  • An oxide which contains the smallest possible proportion of oxygen in relation to the other element (i.e. one in which the other element occurs in its lowest oxidation state).

Origin

Early 19th century; earliest use found in Thomas Thomson (1773–1852), chemist. From proto- + oxide.

Pronunciation

protoxide

/prəʊˈtɒksʌɪd/