Bottom in Eton, I prepared to be disciplined (8)
I believe the answer is:
obedient
'be disciplined' is the definition.
(both can mean well-behaved)
'bottom in eton i prepared' is the wordplay.
'bottom' becomes 'bed' (synonyms).
'in' means one lot of letters goes inside another.
'prepared' indicates anagramming the letters.
'eton'+'i'='etoni'
'etoni' anagrammed gives 'oient'.
'bed' going into 'oient' is 'OBEDIENT'.
'to' acts as a link.
(Other definitions for obedient that I've seen before include "Ready to agree" , "Deferential" , "co-operative?" , "Passive" , "Doing as one's told" .)