Bog paper hiding naughty mag (8)
I believe the answer is:
quagmire
'bog' is the definition.
(I know that quagmire is a type of bog)
'paper hiding naughty mag' is the wordplay.
'paper' becomes 'quire' (paper measurement).
'hiding' means one lot of letters goes inside another.
'naughty' indicates anagramming the letters.
'mag' with letters rearranged gives 'agm'.
'quire' going around 'agm' is 'QUAGMIRE'.
(Other definitions for quagmire that I've seen before include "Problem" , "Area of soft boggy land" , "Swamp" , "Bog; complex situation" , "problematic situation" .)