Source : Webster's Revised Unabridged Dictionary (1913)

Improsperous \Im*pros"per*ous\, a. [Pref. im- not + prosperous:
   cf. F. improsp[`e]re, L. improsper.]
   Not prosperous. [Obs.] --Dryden. -- {Im*pros"per*ous*ly},
   adv. [Obs.] -- {Im*pros"per*ous*ness}, n. [Obs.]