One's associated with a thinly-stretched body that's short of member (7,3)
I believe the answer is:
sausage dog
'one's' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sausage dog that I've seen before include "Dachshund (colloq.)" , "At a stretch, a pet" .)