Dated form of convalescence.

plural of convalescency

(medicine) The blood plasma of a person who has recovered from an infectious illness, which contains antibodies to the infectious disease factor (such as viruses). For convalescent plasma therapy, the plasma can be transfused into an ill victim of that disease as a treatment.

(medicine) A blood serum created from the blood plasma of a person who has recovered from an infectious illness, which contains antibodies to the infectious disease factor (such as viruses). For convalescent serum therapy, the disease antiserum created from the plasma can be injected into an ill victim of that disease as a treatment.