Glimpse dull poseur in the middle and feel strong desire to act (7)
I believe the answer is:
impulse
'to act' is the definition.
(impulse is a kind of act)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for impulse that I've seen before include "I may cause desire" , "Strong urge to act" , "Impel us with sudden urge" , "Sudden urge to act" , "Sudden urge to do something" .)