The Collaborative International Dictionary of English v.0.48:

Plumbous \Plum"bous\, a. [From Plumbum.] (Chem.)
   Of, pertaining to, or containing, lead; -- used specifically
   to designate those compounds in which it has a lower valence
   as contrasted with plumbic compounds.
   [1913 Webster]

WordNet (r) 3.0 (2006):

plumbous
    adj 1: relating to or consisting of lead [syn: plumbic,
           plumbous]