The Collaborative International Dictionary of English v.0.48:

Negotiant \Ne*go"ti*ant\, n. [L. negotians, prop. p. pr. of
   negotiari: cf. F. n['e]gociant.]
   A negotiator. [R.] --Sir W. Raleigh.
   [1913 Webster]

WordNet (r) 3.0 (2006):

negotiant
    n 1: someone who negotiates (confers with others in order to
         reach a settlement) [syn: negotiator, negotiant,
         treater]