She's a left-hander in disguise, showing no real enthusiasm (4-11)

I believe the answer is:

half-heartedness

'showing no real enthusiasm' is the definition.
(half-hearted means showing little enthusiasm)

'she's a left-hander in disguise' is the wordplay.
'in disguise' indicates an anagram.
'shes'+'a'+'left'+'hander'='shesalefthander'
'shesalefthander' is an anagram of 'HALF-HEARTEDNESS'.

I've seen this clue in The Guardian.

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