Put off, being fed up to the bitter end (5)
I believe the answer is:
defer
'put off' is the definition.
(I know that put off can be written as defer)
'fed up to the bitter end' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'to' means one lot of letters go next to another.
'end' suggests the final letters.
The final letters of 'the bitter' are 'er'.
'fed' in reverse letter order is 'def'.
'def'+'er'='DEFER'
'being' is the link.
(Other definitions for defer that I've seen before include "Put off or give way" , "Stay" , "Delay" , "Freed to submit to authority" , "Freed (anag.)" .)