What does costly mean?
Costly is an adjective used to describe something that involves great expense, whether measured in money or in other serious consequences. In its most common sense, it applies to items, projects, or decisions that demand a large outlay: a costly renovation, a costly legal battle. The word also extends beyond finance to describe losses of a graver kind — a costly mistake, a costly victory — where the price is paid in lives, time, or reputation rather than currency. Because of this breadth, costly is a staple of journalism and formal writing, often carrying a tone of regret or warning that the lighter word expensive does not. It derives from the noun cost plus the suffix -ly, and its comparative and superlative forms are costlier and costliest. Understanding costly helps readers grasp how English speakers weigh sacrifice, since the word captures the idea that everything of value exacts some price.
adjectiveCostly means involving great expense; it describes something that costs a lot of money or causes a significant loss of resources. It can also describe a loss or mistake that proves damaging or expensive in non-monetary terms.
- Involving great expense; high in price or requiring significant expenditure.
- Causing serious loss or damage, especially of something other than money (e.g. 'a costly mistake', 'a costly defeat').
"The company's decision to delay the recall proved costly when lawsuits followed."
"Replacing the roof was a costly undertaking, but unavoidable after the storm."
"The general's miscalculation proved costly, costing thousands of lives."
A battle can be 'costly' even if not a penny was spent — the word charges you in whatever currency matters: money, time, or lives.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of costly
Costly was formed in Middle English from the noun cost combined with the adjectival suffix -ly, following the pattern of other quality words such as lovely and friendly. The noun cost itself entered English via Old French from Latin constare, meaning 'to stand at a price'. As a result, costly shares deep roots with words like constant and cost itself, all tracing back to the same Latin verb.
Related word forms
How costly is actually used
Costly is more formal than expensive and often carries a negative connotation, especially when describing losses or mistakes rather than mere price. It frequently appears in journalistic and historical writing about war, error, and consequence.
Easily confused with costly
Expensive refers specifically to high monetary price, whereas costly can also describe losses of time, lives, or reputation.