Animal rights covered by some measures (6)
I believe the answer is:
ferret
'animal' is the definition.
(thesaurus)
'rights covered by some measures' is the wordplay.
'rights' becomes 'rr'.
'covered by' indicates putting letters inside.
'some measures' becomes 'feet' (foot is a kind of measure**).
'rr' put within 'feet' is 'FERRET'.
(Other definitions for ferret that I've seen before include "Small fierce animal used to hunt rabbits" , "Semi-domesticated polecat" , "Tame polecat" , "Animal bred for hunting rats and rabbits" , "Small animal used to drive rabbits from burrows" .)