costing vs cost accounting

costing and cost accounting both are nouns.

Word	Noun	Adjective	Verb	Adverb
costing	Yes	No	No	No
cost accounting	Yes	No	No	No

As nouns, cost accounting is a hypernym of costing; that is, cost accounting is a word with a broader meaning than costing:

costing (noun)	cost accounting (noun)
cost accounting	keeping account of the costs of items in production