The Collaborative International Dictionary of English v.0.48:

Corroborant \Cor*rob"o*rant\ (k?r-r?b"?-rant), a. [L.
   corroborans, p. pr. See Corroborate.]
   Strengthening; supporting; corroborating. --Bacon. -- n.
   Anything which gives strength or support; a tonic.
   [1913 Webster]

         The brain, with its proper corroborants, especially
         with sweet odors and with music.         --Southey.
   [1913 Webster]

WordNet (r) 3.0 (2006):

corroborant
    adj 1: used of a medicine that is strengthening