Scope no.1 climbing target (8)
I believe the answer is:
ambition
'target' is the definition.
(I've seen this before)
'scope no 1 climbing' is the wordplay.
'scope' becomes 'ambit' ('ambit' can be a synonym of 'scope').
'1' becomes 'i' ('i' can be a synonym of '1').
'climbing' says the letters should be written in reverse (in a down clue, letters climb up).
'no'+'i'='noi'
'noi' written backwards gives 'ion'.
'ambit'+'ion'='AMBITION'
(Other definitions for ambition that I've seen before include "A determination to succeed" , "Strong drive for success" , "Strong desire to achieve, fame or fortune" , "Desire to get on" , "Strong desire for success" .)