Strongly urge (6)
I believe the answer is:
exhort
'strongly urge' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for exhort that I've seen before include "Give great encouragement to" , "Spur on" , "Encourage, urge" , "Urge, advise earnestly" , "Urge or advise strongly" .)