Recently Pat Gunning asked the following in response to my Query on avoidable cost: " ...could you give some hints. Aren't all costs avoidable?"
 
The economic answer to that, I think, is that all costs are avoidable in the long run, but some are not avoidable in the short run - i.e. they are fixed.
 
What I am trying to find is the origin of the use of the term "avoided", "avoidable" etc., to describe the opposite of a sunk cost.  "Avoided cost" is a commonly used term in regulatory economics.

Adam McHugh