It's awfully easy to hide a small composition (5)
I believe the answer is:
essay
'composition' is the definition.
(I've seen this in another clue)
'it's awfully easy to hide a small' is the wordplay.
'it's awfully' indicates anagramming the letters.
'to hide' means one lot of letters goes inside another.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'easy' is an anagram of 'esay'.
'esay' going around 's' is 'ESSAY'.
(Other definitions for essay that I've seen before include "Short literary piece: attempt" , "example of Hazlitt's work" , "Make an effort to write one" , "Short treatise" , "Try; a piece of writing" .)