Solitary form of cream (6)
I believe the answer is:
single
'solitary' is the definition.
('single' can be a synonym of 'solitary')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for single that I've seen before include "Ticket To Ride < : > hit" , "Solo" , "Unaccompanied" , "Just one - on one's own" , "Short pop record" .)