Slight exasperation shown about good number (6)
I believe the answer is:
ignore
'slight' is the definition.
(synonyms)
'exasperation shown about good number' is the wordplay.
'exasperation' becomes 'ire' (I've seen this before).
'shown about' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'number' becomes 'no' (abbreviation for 'number').
'g'+'no'='gno'
'ire' enclosing 'gno' is 'IGNORE'.
(Other definitions for ignore that I've seen before include "Cut head off" , "Pass over" , "Region in which to snub" , "'Disregard, overlook (6)'" , "Turn a blind eye to" .)