S for Sovereign (4,2,5)

I believe the answer is:

head of state

's' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

(Other definitions for head of state that I've seen before include "Perhaps monarch" , "leader" , "Putin, say" .)

I've seen this clue in The Guardian and The Times.

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