Can it go on spreading? (9)
I believe the answer is:
Here is my best explanation:
'can it go on spreading?' is the definition.
I can't tell whether this defines the answer.
'can it go on spreading?' is the wordplay.
'spreading?' indicates anagramming the letters.
'canitgoon' with letters rearranged gives 'CONTAGION'.
(Other definitions for contagion that I've seen before include "Infection", "Cognation (anag.)", "Communication of disease by close contact" and "cause of widespread ill-feeling".)