Opportunity cost
Etymology
A compound from economics. "Opportunity" traces to Latin ob portum, the idea of a wind bringing a ship "toward the harbour" — a favorable moment. "Cost" is from Latin constare, "to stand at (a price)." Together they name the cost measured in foregone opportunities rather than cash.
noun · /op-er-TOO-nih-tee kost/
The value of the best alternative you give up when you choose one option over another.
What it names
The hidden price of every choice — not what you paid, but what you could have done instead.
Example
The real opportunity cost of the meeting wasn’t the hour; it was the deep work that hour would have bought.
Related idea
Sunk cost looks backward at what’s already spent; opportunity cost looks sideways at what you’re giving up now.