resign

To resign is to give up power, to voluntarily quit a job or come to terms with something as unavoidable. (verb)

When you decide to leave your position and write your boss a letter letting him know, this is an example of a situation where you resign from your position.
When you know you are going to lose money on a deal and you accept that fact, this is an example of a situation where you resign yourself to loss.

See resign in Webster's New World College Dictionary

See resign in American Heritage Dictionary 4