Class can be added to first to form a compound adjective
A compound adjective is a type of adjective formed when two or more adjectives are joined together. 
An adjective qualifies a noun
Examples of compound adjectives
- First-class 
- Four-foot 
- Part-time
- Cold-blooded
First-class means something that is of the highest quality. 
For example, The drink is first-class
It means that the drink is of the highest quality
To learn more about compound adjectives, please check: brainly.com/question/2985406?referrer=searchResults