We found 11 dictionaries that define the word costliest:

General (10 matching dictionaries)

1. costliest: Merriam-Webster
2. costliest: Oxford Learner's Dictionaries
3. costliest: Collins English Dictionary
4. costliest: Vocabulary.com
5. Costliest, costliest: Wordnik
6. costliest: Cambridge Advanced Learner's Dictionary
7. costliest: Wiktionary
8. costliest: Dictionary.com
9. costliest: Cambridge Essential American English Dictionary
10. costliest: TheFreeDictionary.com

Business (1 matching dictionary)

11. costliest: Legal dictionary

(Note: See costly as well.)

Definitions from Wiktionary (costly) ▸ adjective:  Of high cost; expensive. ▸ Also see costly ▸ Words similar to costliest ▸ Usage examples for costliest ▸ Idioms related to costliest ▸ Wikipedia articles (New!) ▸ Popular nouns described by costliest ▸ Words that often appear near costliest ▸ Rhymes of costliest ▸ Invented words related to costliest