Roman Catholics can count on it (6)
I believe the answer is:
rosary
'roman catholics can' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'count on it' is the wordplay.
'count' becomes 'rory' (I can't justify this - if you can you should believe this answer much more).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'rory' going around 'sa' is 'ROSARY'.
Can you help me to learn more?
(Other definitions for rosary that I've seen before include "String of devotional beads" , "RC beads" , "Prayer bead set" , "Series of prayers" , "String of beads for counting prayers" .)