Bores a doctor with ailments (6)
I believe the answer is:
drills
'bores' is the definition.
(I know this)
'a doctor with ailments' is the wordplay.
'a doctor' becomes 'Dr' (abbreviation).
'with' means one lot of letters go next to another.
'ailments' becomes 'ills' ('ill' can be a synonym of 'ailment').
'dr'+'ills'='DRILLS'
(Other definitions for drills that I've seen before include "they bore" , "Teaches by repetition" , "Bores in army exercises" , "monkeys" , "Potato rows" .)