One sleeping reportedly in sheepskin (4)
I believe the answer is:
napa
'sheepskin' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'one sleeping reportedly' is the wordplay.
'one sleeping' becomes 'nap' (nap is a kind of sleeping).
'reportedly' becomes 'a' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'nap'+'a'='NAPA'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for napa that I've seen before include "soft skin" , "California wine valley" , "Californian valley, famous for wine" .)