Medical help if you lose heart and cave, in, possibly? (7)
I believe the answer is:
vaccine
'medical' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for vaccine that I've seen before include "preparation for pandemic?" , "Vice can create protection against disease" , "Antibody stimulator" , "Immunity stimulant" , "Antigenic preparation" .)