Might war prisoner, perhaps, when meeting the queen? (5)
I believe the answer is:
power
'might' is the definition.
('power' can be a synonym of 'might')
'war prisoner perhaps when meeting the queen?' is the wordplay.
'war prisoner perhaps' becomes 'pow' (abbreviation for 'prisoner of war').
'when meeting' says to put letters next to each other.
'the queen?' becomes 'er' (Elizabeth Regina).
'pow'+'er'='POWER'
(Other definitions for power that I've seen before include "index" , "Electricity or strength" , "Military potential" , "Strength - capacity" , "Supply with energy" .)