renounce (v)
relinquish (v)
quit (v)
foreswear (v)

Definition: turn away from
Example: I am foreswearing women forever.

take leave (v)
quit (v)
depart (v)

Definition: go away or leave

chuck up the sponge (v)
drop by the wayside (v)
drop out (v)
fall by the wayside (v)
give up (v)
quit (v)
throw in (v)
throw in the towel (v)

Definition: give up in the face of defeat of lacking hope
Example: In the second round, the challenger gave up.

step down (v)
resign (v)
quit (v)
leave office (v)

Definition: give up or retire from a position
Example: The Secretary of the Navy will leave office next month. The chairman resigned over the financial scandal.

cease (v)
discontinue (v)
give up (v)
lay off (v)
quit (v)
stop (v)

Definition: put an end to a state or an activity
Example: Quit teasing your little brother.