Describes medication counteracting rapid spreading (9)
I believe the answer is:
antiviral
'spreading' is the definition.
Both the definition and answer are adjectives.
Perhaps you can see a link between them that I don't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for antiviral that I've seen before include "inhibiting disease" , "Like interferons" , "Drug" , "describing security software?" .)