/ ˈkɒstli; NAmE ˈkɔːst-/ adjective ( cost·lier , cost·li·est )
HELP NOTE : You can also use more costly and most costly .
1.
costing a lot of money, especially more than you want to pay
SYN expensive :
Buying new furniture may prove too costly.
➡ note at expensive
2.
causing problems or the loss of sth
SYN expensive :
a costly mistake / failure
Mining can be costly in terms of lives (= too many people can die) .
► cost·li·ness noun [ U ]