Reservations rejected in the end (4)
I believe the answer is:
stub
'the end' is the definition.
(eg the stub of a cigarette)
'reservations rejected' is the wordplay.
'reservations' becomes 'buts' (I've seen this in another clue).
'rejected' says the letters should be written in reverse.
'buts' in reverse letter order is 'STUB'.
'in' acts as a link.
(Other definitions for stub that I've seen before include "A short stump as of cigar" , "Short bit of pencil, say" , "Short end" , "Strike one's toe accidentally (against something)" , "Remnant, butt" .)