Intensify, increase rapidly (8)
I believe the answer is:
escalate
I believe this is a double definition.
'intensify' is the first definition.
(I know that intensify can be written as escalate)
'increase rapidly' is the second definition.
(I've seen this before)
(Other definitions for escalate that I've seen before include "Quickly increase in scale" , "Increase in intensity or extent, like trouble brewing" , "Amplify" , "mount in tension" , "Magnify" .)