protoxide

noun

1. Any of a series of oxides of a particular metal that has the fewest atoms of oxygen per molecule

   “Oxy­gen frequently combines in various proportions with a substance, rendering it an oxide, but without advancing it to the state of an acid. In order to distinguish each compound thus formed, the language of chemistry is very systematic. The first is called a protoxide; the second a deutoxide; and the third, a paroxide.”