Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
plumbāgo, ĭnis, f. [plumbum]. 
- I.  A species of lead ore, black-lead, plumbago, also called molybdaena, Plin. 34, 18, 50, § 168.
 
- B.  Transf., a leaden color in gems, Plin. 37, 5, 18, § 68.
 
- II.  A plant, also called molybdaena, leadwort, fleawort, Plin. 25, 13, 97, § 155.