The Collaborative International Dictionary of English v.0.48:

Convalesce \Con`va*lesce"\, v. i. [imp. & p. p. Convalesced;
   p. pr. & vb. n. Convalescing.] [L. convalscere; con- +
   valescere to grow strong, v. incho. of valere to be strong.
   See Valiant.]
   To recover health and strength gradually, after sickness or
   weakness; as, a patient begins to convalesce.
   [1913 Webster]

WordNet (r) 3.0 (2006):

convalesce
    v 1: get over an illness or shock; "The patient is recuperating"
         [syn: recuperate, recover, convalesce] [ant:
         degenerate, deteriorate, devolve, drop]