Dissent remains after new uniform rejected (6)
I believe the answer is:
unrest
'dissent' is the definition.
(dissent can mean disruption or unrest)
'remains after new uniform rejected' is the wordplay.
'remains' becomes 'rest' (both can mean what's left over).
'after' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'rejected' shows that the letters should be reversed in order.
'n'+'u'='nu'
'nu' backwards is 'un'.
'rest' after 'un' is 'UNREST'.
(Other definitions for unrest that I've seen before include "Disorder" , "State of rebellion" , "Discontent, disturbance" , "'Discontent, anxiety (6)'" , "Uneasiness; turmoil" .)