The Collaborative International Dictionary of English v.0.48:

Desinent \Des"i*nent\, a. [L. desinens, p. pr. of desinere,
   desitum, to leave off, cease; de- + sinere to let, allow.]
   Ending; forming an end; lowermost. [Obs.] "Their desinent
   parts, fish." --B. Jonson.
   [1913 Webster]