Hypo

A prefix from the Greek preposition ὑπό, under, beneath, and frequently used in composition to signify a less quantity, or a low state or degree of that denoted by the word with which it is joined, position under or beneath it, and the like. In chemical language, prefixed to the name of a compound containing oxygen, it designates another compound containing less oxygen; as, hypo-nitrous acid, which contains less oxygen than nitrous acid.