Charles the Third in pursuit? (5)
I believe the answer is:
chase
'pursuit?' is the definition.
(synonyms)
'charles the third' is the wordplay.
'charles' becomes 'Chas' (shortened form).
'the third' becomes 'e' (3rd letter of 'the').
'chas'+'e'='CHASE'
'in' acts as a link.
(Other definitions for chase that I've seen before include "Composed type accommodated in this" , "Follow" , "Pursue, run after" , "Pursuit" , "groove" .)