back down

1.  Reverse one's upward course, descend. For example, When she saw the wasps' nest on the roof, she hastily backed down the ladder. This literal usage usually refers to something one has climbed, such as a ladder or mountain. [Mid-1800s]
2.  Also, back off. Retreat or yield. For example, As the watchdog began to snarl the letter carrier backed off, or You have a good point; now don't back down when you present it to the board. [First half of 1900s] Also see back away, def. 2.

Definition: withdraw from agreement or statement
Antonyms: go forward

The verb has 2 meanings:

Meaning #1: move backwards from a certain position
  Synonyms: back up, back off

Meaning #2: remove oneself from an obligation
  Synonyms: chicken out, back off, pull out, bow out