Cost/kɔːst/ Definition 1 of 4Pro Tip 1/3Fixed Price When discussing cost as a verb, the price given is usually non-negotiable, as in a store price tag. How much does this book cost? Pro Tip 2/3Hypothetical Transactions Use 'cost' to discuss the price of hypothetical or future purchases or actions. Renting a larger apartment would cost more. Pro Tip 3/3Past Purchases For things already bought, use 'cost' to indicate the money spent in the past. The wedding cost us a small fortune.