Suffer small discolouration covering uniform (7)
I believe the answer is:
sustain
'suffer' is the definition.
(I know that suffer can be written as sustain)
'small discolouration covering uniform' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'discolouration' becomes 'stain' (synonyms).
'covering' means one lot of letters goes inside another.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
's'+'stain'='sstain'
'sstain' enclosing 'u' is 'SUSTAIN'.
(Other definitions for sustain that I've seen before include "Provide nourishment" , "Give food to" , "Keep (something) going" , "Support, keep going" , "Withstand" .)