English Reference
adjective

costly

adj.
US /ˈkɑstɫi/ UK /kˈɒstli/ cost·ly

  1. 01 B2 Upper Intermediate

    costing a lot of money.

    of high cost; expensive. Often used to imply that the price is higher than expected or justified.

    Simple

    Buying a new car can be very costly when you include insurance.

    In context

    The renovation proved more costly than the initial estimates suggested, forcing the family to dip into their long-term savings.

    Pitfall
    The repair was very costly for me. The repair was very costly.

    While 'expensive' often takes 'for someone', 'costly' is usually used as a direct description of the item or event itself.

  2. 02 C1 Advanced Formal

    causing a lot of problems, damage, or the loss of something important.

    resulting in great loss, damage, or sacrifice; having negative consequences that are difficult to recover from.

    Simple

    A costly mistake at work resulted in the company losing a big client.

    In context

    The general's decision to delay the retreat proved to be a costly error that resulted in heavy casualties.

Usage costly items

Governments have pledged costly aid packages to help the sector.

The Guardian· 17 Aug 2026

Erin says when she posted about her costly decision over fertility treatment, she got thousands of comments from people who "can't believe this is even a thing".

BBC News· 17 Aug 2026

From Middle English costly, costely, costeley, equivalent to cost + -ly.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Middle English costly
Level C1 · Advanced
Frequency Frequent
Updated