Sentence:  As trust in government declines, it becomes more and more difficult to make effective use of state power. For nonprofit and voluntary organizations, these issues do not arise. Free choice is the <WSD>coin of the realm</WSD>: Donors give because they choose to do so. Volunteers work of their own volition. 
Meaning of the word marked with <WSD> tags:  Something that is valued like money within a particular context.