New job dress code 'Modestly dressed' - help

[Ratley]

Hi,
I start my new job as a cover supervisor in a secondary school in September, I emailed asking for dress code and was told "staff must be modestly dressed" I have no idea what that means outside of knees and cleavage covered, are shoulders allowed.
Also I have always worked outdoors so don't even have basics like black trousers. I went to the interview in my 'funeral suit' I am very aware of not wanting to look like a teacher (so wouldn't rock up in a business suit) as I don't want to break some unwritten hierarchy rules but equally I don't want to be underdressed.
PS this is a Catholic school in the North East.
Any thoughts?

Thank you princess my job is in a specific department (maths) so it probably leans more to the smart. I'm not very comfortable in shirts. I think I should observe what the other staff wear for the first few weeks,

Thank you Bertrand - so glad it's not just me. It also seems to be increasingly used euphemistically in the context of cultures which are not renowned for their embracing of female sexuality. I hate the way that the usage of the word 'modest' is becoming restricted to the concealment of a woman's body, as though, by implication, that is the primary asset she has to boast about.

The three t's is a good rule for everywhere except beach, night out or at home - plus trousers that fit so no bum on show when bending over.

Both genders too. Put it away, thank you .