Act of lust a hindrance to companion (5)

I believe the answer is:

letch

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'act of lust' is the definition.
The definition suggests a singular noun which matches the answer.

'a hindrance to companion' is the wordplay.
'a hindrance' becomes 'let' (let can mean an obstruction).
'to companion' becomes 'ch' (Companion of Honour).
'let'+'ch'='LETCH'

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I've seen this clue in The Guardian.

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