Athena
The word "mew" derives from the Latin word mūtāre, to change, which also gives us our English word mutate. But mew is now only used in reference to a particular type of change – the molting of a bird when it loses its old feathers and grows new ones.
Ralph
Because a bird can’t fly during this process, the owner of a valuable hunting falcon would keep it “mewed” up – that is, confined in a protective enclosure where it would be safe from predators. 
Here, Theseus is using mew in a figurative sense, to describe nuns secluded in a convent to protect them from male predators.