found: Work cat.: Sutton, J. Sunk costs and market structure, c1991.
found: Bantock, G. Dictionary of economics, 1998(Sunk costs. Opportunity costs incurred in the past which are irretrievable and therefore not relevant to current decisions.)
found: Shim, J.K. Dictionary of economics, 1995(Sunk cost. The cost of resources ... incurred in the past whose total will not be affected by any decision made now or in the future.)
found: Macmillan dictionary of modern economics, 1992(Sunk costs. Costs which cannot be recovered when a firm leaves an industry.)