Pressure concerning young claimant to the throne (9)
I believe the answer is:
pretender
'claimant to the throne' is the definition.
(I've seen this before)
'pressure concerning young' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'concerning' becomes 're'.
'young' becomes 'tender' (similar in meaning).
'p'+'re'+'tender'='PRETENDER'
(Other definitions for pretender that I've seen before include "Claimant, like Bonnie Prince Charlie" , "One who claims a title or position" , "Claimant to a throne, usually without just title" , "fake" , "One acting" .)