Could it be confusing to an Irish student of old? (9)
I believe the answer is:
historian
'student of old?' is the definition.
(student of the past)
'could it be confusing to an irish' is the wordplay.
'could it be confusing' indicates an anagram (letters get confused).
'to'+'an'+'irish'='toanirish'
'toanirish' is an anagram of 'HISTORIAN'.
(Other definitions for historian that I've seen before include "chronicler" , "Past master" , "Writer about the past" , "So thin air suits recorder and analyst of past events" , "One sort of academic" .)