Beginning with any number climbing (7)
I believe the answer is:
nascent
'beginning' is the definition.
(I've seen this before)
'with any number climbing' is the wordplay.
'with' means one lot of letters go next to another.
'any number' becomes 'n' (I've seen this in other clues).
'climbing' becomes 'ascent' (I've seen this before).
'n' next to 'ascent' is 'NASCENT'.
(Other definitions for nascent that I've seen before include "Freshly generated" , "Coming into existence" , "Developing" , "Being born - scan net (anag)" , "being coined" .)