Was I not AB? Perhaps I was! (9)
I believe the answer is:
'i was' is the definition.
I can't tell whether this defines the answer.
'was i not ab? perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'wasinotab' is an anagram of 'BOATSWAIN'.
Can you help me to learn more?
(Other definitions for boatswain that I've seen before include "A fully developed bo'sun" , "Merchant ship's petty officer" , "I was not AB (anag) - naval warrant officer" , "One at sea" , "Warrant officer in charge of a ship's crew" .)