Carthaginian pun, I see (5)
I believe the answer is:
punic
'carthaginian' is the definition.
(synonyms)
'pun i see' is the wordplay.
'see' becomes 'C' (the word for the letter, according to Chambers).
'pun'+'i'+'c'='PUNIC'
(Other definitions for punic that I've seen before include "Relating to Carthage" , "Carthaginian" , "ancient language" .)