I long to grow contained but lively (5)
I believe the answer is:
agile
'lively' is the definition.
(thesaurus)
'i long to grow contained' is the wordplay.
I cannot quite see how this works, but
'i' could be 'a' and 'a' is found within the answer.
'long' could be 'l' and 'l' is found in the answer.
The remaining letters 'gie' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'but' acts as a link.
Can you help me to learn more?
(Other definitions for agile that I've seen before include "Flexible" , "Nimble, spry" , "Limber" , "Nimble, supple" , "Nimble, lithe" .)