Rural boy starting to undergo abdominal pain (7)
I believe the answer is:
bucolic
'rural' is the definition.
(similar in meaning)
'boy starting to undergo abdominal pain' is the wordplay.
'boy' becomes 'b' (abbreviation used in schools).
'starting to' indicates taking the first letters.
'abdominal pain' becomes 'colic' (I've seen this before).
The initial letter of 'undergo' is 'u'.
'b'+'u'+'colic'='BUCOLIC'
(Other definitions for bucolic that I've seen before include "Rustic - pastoral" , "Pastoral poem" , "Of rural or pastoral life" , "Agrarian" , "Relating to rural life" .)