Cardinal and Father exiting carriage (5)
I believe the answer is:
eight
'cardinal' is the definition.
(eight is a cardinal number)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for eight that I've seen before include "Several in a row" , "23" , "Cube root of five hundred and twelve" , "Pints in gallon" , "What's next?" .)