Cardinal studied, we hear? (3)
I believe the answer is:
red
'cardinal' is the definition.
(thesaurus)
'studied we hear?' is the wordplay.
'studied' becomes 'read' (I've seen this before).
'we hear?' indicates a 'sounds like' (homophone) clue.
'read' is a homophone of 'RED'.
(Other definitions for red that I've seen before include "Scarlet or vermilion" , "Crimson" , "- Cross; - admiral" , "Merchant flag" , "Left-wing" .)