Strange as sheep could be, but not goats (8)
I believe the answer is:
singular
'strange' is the definition.
(similar in meaning)
'as sheep could be but not goats' is the wordplay.
I cannot really understand how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for singular that I've seen before include "Individual; extraordinary" , "Unusual - not plural" , "Unique, peculiar" , "Unique - nails rug (anag)" , "number" .)