-uous
(juːəs)
a compound suffix, repr. L. -uōs-us (-a, -um), OF. or AF. -uous, -uos (F. -ueux), occurring in a number of adoptions from L. (or F.), as fructuous, halituous, impetuous, † monstruous, † portentuous, sumptuous, tempestuous, virtuous; and hence by analogy employed with the sense ‘of the nature of, consisting of’ in a few E. formations on L. stems, as ambiguous (1528–), strenuous (1599–), † subsiduous (1490), torrentuous (1840–).
By assimilation, OE. rihtw{iacu}s (‘righteous’) became rightuous in the 15–16th c.