Should be nothing without a leader (5)
I believe the answer is:
ought
'should be' is the definition.
(I've seen this before)
'nothing without a leader' is the wordplay.
'nothing' becomes 'nought' (synonyms).
'without a leader' means to remove the first letter.
'nought' with its first letter removed is 'OUGHT'.
(Other definitions for ought that I've seen before include "Be logically necessary" , "Should, had, better" , "Be bound" , "Have/has a duty (to do)" , "Tough (anag)" .)