Minute area covered by minute juvenile cow? (8)
I believe the answer is:
ruminant
'cow?' is the definition.
(cow is a kind of ruminant)
'minute area covered by minute juvenile' is the wordplay.
'minute' becomes 'min' (abbreviation).
'area' becomes 'a' (maths abbreviation).
'covered by' means one lot of letters goes inside another.
'minute juvenile' becomes 'runt' (the smallest animal in a litter).
'min'+'a'='mina'
'mina' inserted within 'runt' is 'RUMINANT'.
(Other definitions for ruminant that I've seen before include "Goat, say" , "Cud-chewing animal" , "Cud chewer" , "contemplating" , "Cud chewing mammal" .)