Waxing the top assumes endless money (8)
I believe the answer is:
crescent
'waxing' is the definition.
(thesaurus)
'top assumes endless money' is the wordplay.
'top' becomes 'crest' (crest can mean the top of a hill).
'assumes' is an insertion indicator.
'endless money' becomes 'cen' (I can't justify this - if you can you should believe this answer much more).
'crest' enclosing 'cen' is 'CRESCENT'.
'the' is the link.
Can you help me to learn more?
(Other definitions for crescent that I've seen before include "Curved row of houses" , "Way" , "Turkish emblem" , "Young-moon shape" , "Shape of new(ish) moon" .)