Dynamic police getting terrible flu (8)
I believe the answer is:
forceful
'dynamic' is the definition.
(similar in meaning)
'police getting terrible flu' is the wordplay.
'police' becomes 'force' (the force can refer to the police force).
'getting' is a charade indicator (letters next to each other).
'terrible' is an anagram indicator.
'flu' with letters rearranged gives 'ful'.
'force'+'ful'='FORCEFUL'
(Other definitions for forceful that I've seen before include "Persuasive" , "Emphatic. assertive" , "Powerful, assertive" , "Assertive, vigorous" , "Full of strength" .)