At the start of an affair, she makes a bundle (5)
I believe the answer is:
sheaf
'a bundle' is the definition.
('sheaf' can be a synonym of 'bundle')
'at the start of an affair she makes' is the wordplay.
'at' means one lot of letters go next to another.
'the start of' indicates taking the first letters.
'makes' becomes 'f' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'affair' is 'a'.
'a' put after 'she' is 'shea'.
'shea'+'f'='SHEAF'
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" .)