to/until the bitter end

:  to

: used as a function word to indicate continuance (as of an action or condition) to a specified time

:  before

:  up to the time that :  up to such time as

:  being or inducing the one of the four basic taste sensations that is peculiarly acrid acrid, astringent, or disagreeable and suggestive of an infusion of hops — compare salt, sour, sweet

:  distasteful or distressing to the mind :  galling

:  marked by intensity or severity:

:  bitter (see ¹bitter) quality

:  a usually alcoholic solution of bitter and often aromatic plant products used especially in preparing mixed drinks or as a mild tonic (see ¹tonic 1b)

:  a very dry (see ¹dry 7b) heavily hopped ale

:  to make bitter (see ¹bitter)

:  to an intense or severe degree :  to a bitter (see ¹bitter) degree

:  the part of an area that lies at the boundary

:  a point that marks the extent of something

:  the point where something ceases to exist

:  to bring to an end

:  destroy

:  to make up the end of

:  final, ultimate

:  to put (grain or hay) into a barn or stack