IPA: /ˈkɔːstlinəs/
KK: /ˈkɔstlɪnəs/
The quality or state of being expensive or having a high price.
The costliness of the new smartphone made many people reconsider their purchase.
Costliness → It is formed from "cost" (from Old French *coste*, meaning expense or price) and "-liness" (meaning the quality of being). The word "costliness" refers to the quality of being expensive or having a high price.
Think of the word 'cost' which relates to expense, and remember that 'costliness' means the quality of being expensive.