Unending advice not to jump about so much (9)
I believe the answer is:
boundless
'unending' is the definition.
(thesaurus)
'advice not to jump about so much' is the wordplay.
I cannot quite see how this works, but
'not' could be 'less' (I've seen this in other clues) and 'less' is found in the answer.
'jump' could be 'bound' (bounding is a kind of jumping) and 'bound' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for boundless that I've seen before include "Unlimited" , "Having no limit, extensive" , "Without limits" , "Seemingly without limit" .)