Expose the flaw of beach on holiday (5,3)
I believe the answer is:
catch out
'holiday' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how one could define the other.
'expose the flaw of beach on' is the wordplay.
'expose' becomes 'out' (outing is a kind of exposing).
'the flaw of beach' becomes 'catch' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on' says to put letters next to each other.
'out' after 'catch' is 'CATCH OUT'.
Can you help me to learn more?
(Other definitions for catch out that I've seen before include "Trap" , "Detect in a mistake or deceit" , "Detect in a mistake - gotcha" , "detect in error" .)