To become healthy and strong again slowly over time after illness, weakness, or injury
1) He is convalescing from his leg injuries.
2) The soldier spent long months in the hospital in order to convalesce.
From Latin convalescere which means 'to grow strong'.
gain, heal, mend, recoup, recover, rally, recuperate, pull round
deteriorate, decline, relapse, decay, degenerate, demolish