Roman Catholic in love concealed plant (6)
I believe the answer is:
orchid
'plant' is the definition.
(orchid is a kind of plant)
'roman catholic in love concealed' is the wordplay.
'roman catholic' becomes 'rc' (abbreviation for Roman Catholic).
'in' means one lot of letters goes inside another.
'love' becomes 'o' (love means zero in tennis).
'concealed' becomes 'hid' ('hide' can be a synonym of 'conceal').
'o'+'hid'='ohid'
'rc' placed within 'ohid' is 'ORCHID'.
(Other definitions for orchid that I've seen before include "Expensive, perfumed flower" , "Exotic flower with strong perfume" , "Prized exotic plant" , "Common houseplant" , "Light bluish red" .)