NOUN (2)

1. recuperation in which the symptoms of an acute disease gradually subside;

2. (biochemistry) dissolution or destruction of cells such as blood cells or bacteria;

The Collaborative International Dictionary of English v.0.48:

Lysis \Ly"sis\ (l[imac]"s[i^]s), n. [NL., fr. Gr. ly`sis.]
   (Med.)
   The resolution or favorable termination of a disease, coming
   on gradually and not marked by abrupt change.
   [1913 Webster]

   Note: It is usually contrasted with crisis, in which the
         improvement is sudden and marked; as, pneumonia ends by
         crisis, typhoid fever by lysis.
         [1913 Webster]