The Collaborative International Dictionary of English v.0.48:

Aptote \Ap"tote\ ([a^]p"t[=o]t), n. [L. aptotum, Gr. ?
   indeclinable; 'a priv. + ? fallen, declined, ? to fall.]
   (Gram.)
   A noun which has no distinction of cases; an indeclinable
   noun.
   [1913 Webster]