Faulty service by prince can be deadly (6)
I believe the answer is:
lethal
'be deadly' is the definition.
(synonyms)
'faulty service by prince' is the wordplay.
'faulty service' becomes 'let' (type of tennis serve. I am not sure about the 'faulty' bit.).
'by' is a charade indicator (letters next to each other).
'prince' becomes 'hal' (Shakespearean nickname of Henry V when a prince).
'let'+'hal'='LETHAL'
'can' is the link.
Can you help me to learn more?
(Other definitions for lethal that I've seen before include "Destructive" , "Deadly dangerous" , "Killing" , "Noxious" , "Able to cause death" .)