Political leader holds back gentleman, a solid figure (5)
I believe the answer is:
prism
'a solid figure' is the definition.
(I've seen this before)
'political leader holds back gentleman' is the wordplay.
'political leader' becomes 'PM' (abbreviation for prime minister).
'holds' indicates putting letters inside.
'back' shows that the letters should be reversed in order.
'gentleman' becomes 'sir' (a man may be addressed as sir).
'sir' backwards is 'ris'.
'pm' going around 'ris' is 'PRISM'.
(Other definitions for prism that I've seen before include "Glass triangle, separates light into colours" , "Refracting glass" , "Light-bending glass" , "Female character in The Importance of Being Earnest - optical device" , "Light transmitter" .)