Not very big manuscript put up by everybody (5)
I believe the answer is:
small
'not very big' is the definition.
(big is the opposite of small)
'manuscript put up by everybody' is the wordplay.
'manuscript' becomes 'ms' (abbreviation for manuscript).
'put up' says the letters should be written backwards.
'by' is a charade indicator (letters next to each other).
'everybody' becomes 'all' (all people).
'ms' reversed gives 'sm'.
'sm'+'all'='SMALL'
(Other definitions for small that I've seen before include "Of little size" , "of little significance" , "Piddling" , "Not great (in number)" , "Diminutive" .)