Group of big cats putting pressure on horse, possibly (5)
I believe the answer is:
pride
'group of big cats' is the definition.
(group of lions)
'pressure on horse possibly' is the wordplay.
'pressure' becomes 'p' (scientific abbreviation).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'horse possibly' becomes 'ride' (animal that can be ridden).
'p'+'ride'='PRIDE'
'putting' is the link.
(Other definitions for pride that I've seen before include "Dignity" , "group of animals" , "Novel by Jane Austen" , "They say it comes before a fall" , "Vanity" .)