(col.) A brothel.
The term is not as popular now as it was in Elizabethan times when nuns had more dubious reputations than they do now.
When Hamlet says to Ophelia ‘Get thee to a nunnery’ (Hamlet [III. i. 124]) it is clear from the context that he is using the word in this sense.
– Wordsworth Dictionary of Obscenity & Taboo by James McDonald.