Solitary form of cream (6)

I believe the answer is:

single

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'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" .)

I've seen this clue in The Mirror.

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