Challenging circuit is to lap old university (9)
I believe the answer is:
ambitious
'challenging' is the definition.
(synonyms)
'circuit is to lap old university' is the wordplay.
I cannot really understand how this works, but
'circuit' could be 'ambit' (I've seen this in another clue) and 'ambit' is found in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found in the answer.
'university' could be 'u' (abbreviation for university) and 'u' is located in the answer.
'is' is within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ambitious that I've seen before include "Seeking success" , "Aspiring" , "Bold - pushy" , "Aspirant" , "Having a strong desire for success" .)