asthenic

from WordNet (r) 3.0 (2006)

asthenic
    adj 1: lacking strength or vigor [syn: {adynamic}, {asthenic},
           {debilitated}, {enervated}]
    2: having a slender physique

from The Collaborative International Dictionary of English v.0.48

Asthenic \As*then"ic\, a. [Gr. 'asqeniko`s; 'a priv. + sqe`nos
   strength.] (Med.)
   Characterized by, or pertaining to, debility; weak;
   debilitating.
   [1913 Webster]