The Collaborative International Dictionary of English v.0.48:

Cuprous \Cu"prous\ (k?"pr?s), a. [From Cuprum.] (Chem.)
   Of, pertaining to, or derived from, copper; containing
   copper; -- said of those compounds of copper in which this
   element is present in its highest proportion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cuprous
    adj 1: of or containing divalent copper [syn: cupric,
           cuprous]