At the start of an affair, she makes a bundle (5)
I believe the answer is:
sheaf
'a bundle' is the definition.
(synonyms)
'at the start of an affair she' is the wordplay.
'at the start of' means one lot of letters go next to another.
'an affair' becomes 'af' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'af' put after 'she' is 'SHEAF'.
'makes' is the link.
Can you help me to learn more?
(Other definitions for sheaf that I've seen before include "Bundle, as of reeds for thatching" , "Bundle of wheat" , "Bundle of cereal plants" , "Stack, bundle" , "Reaper's bundle" .)