Hy"po- (?). [Gr. under, beneath; akin to L. sub. See Sub-.]
A prefix signifying a less quantity, or a low state or degree, of that denoted by the word with which it is joined, or position under or beneath.
A prefix denoting that the element to the name of which it is prefixed enters with a low valence, or in a low state of oxidization, usually the lowest, into the compounds indicated; as, hyposulphurous acid.
© Webster 1913.