monoptote

from The Collaborative International Dictionary of English v.0.48

Monoptote \Mon"op*tote\, n. [L. monoptotum, Gr. mono`ptwtos;
   mo`nos single + ? apt to fall, fallen, fr. ? to fall; cf. ?
   case.] (Gram.)
   1. A noun having only one case. --Andrews.
      [1913 Webster]

   2. A noun having only one ending for the oblique cases.
      [1913 Webster]