Isolation unsettling Spenser at sea (12)
I believe the answer is:
separateness
'isolation' is the definition.
(thesaurus)
'unsettling spenser at sea' is the wordplay.
'unsettling' indicates anagramming the letters.
'spenser'+'at'+'sea'='spenseratsea'
'spenseratsea' is an anagram of 'SEPARATENESS'.
I've seen this clue in The Times.
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