Red key (8)
I believe the answer is:
cardinal
I believe this is a double definition.
'red' is the first definition.
(I know that cardinal is a type of red)
'key' is the second definition.
(synonyms)
(Other definitions for cardinal that I've seen before include "Vivid red of a senior bishop?" , "first" , "Leading RC dignitary" , "cleric" , "Senior Roman Catholic" .)