5d looks more like 'prep' to me but, being rubbish at cryptics, I can't fully parse it:
Prep = 'preposition' (part of speech) in short.
Also, prep = 'get ready' (as when a chef 'preps' vegetables)
Theatre = 'rep' (???) but that still leaves me trying to put 'p' in front of it.
Oh well, I said I'm rubbish at cryptics, so I'm probably not only barking up the wrong tree but also in the wrong forest!
In a dictionary, a preposition is prefaced by the abbreviation 'prep'. Patients are 'prepped' for operations (in an operating theatre'). Sorry, Mr-Hobble, but 'rep' (sometimes used in crosswords for 'theatre', admittedly) is a red herring here.