Study, as I said (3)
I believe the answer is:
eye
'study' is the definition.
(both can mean to examine)
'i said' is the wordplay.
'said' indicates a 'sounds like' (homophone) clue.
'i' is a homophone of 'EYE'.
'as' is the link.
(Other definitions for eye that I've seen before include "Watch - middle of cyclone" , "Watch closely" , "Four [NEEDLEFUL] may pass through this" , "'Cast a cold ... on life, on death' (Yeats)" , "Bit of a potato (or a needle?)" .)