The Collaborative International Dictionary of English v.0.48:

Conatus \Co*na"tus\, n. [L., fr. conatus, p. p. of conari to
   attempt.]
   A natural tendency inherent in a body to develop itself; an
   attempt; an effort.
   [1913 Webster]

         What conatus could give prickles to the porcupine or
         hedgehog, or to the sheep its fleece?    --Paley.
   [1913 Webster]