Fifty-one assigned to cat? Over forty fewer? (8)
I believe the answer is:
lifeline
'forty fewer?' is the definition.
I can't judge whether this defines the answer.
'fifty-one assigned to cat?' is the wordplay.
'fifty one' becomes 'LI' (Roman numerals).
'assigned to' means one lot of letters go next to another.
'cat?' becomes 'feline' (cat is a kind of feline).
'li'+'feline'='LIFELINE'
'over' is the link.
Can you help me to learn more?
(Other definitions for lifeline that I've seen before include "Essential means of support" , "Vital safeguard" , "Means of escape" , "rescue operation?" , "Essential support (read by palmists?)" .)