first class

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The first, highest, or best group in a system of classification.
• noun The most luxurious and most expensive class of accommodations on a commercial airplane, train, passenger ship, or other conveyance.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Belonging to the best or top group in a system of classification.
• adjective Of, or relating to the most luxurious and expensive class of accommodation on a train, ship, hotel, etc.
• adjective Of, or relating to a class of mail to be delivered before second class.
• adjective cricket Of, or relating to a first class match.
• adjective programming Of, or relating to a treatment like that for a first-class citizen.
• proper noun A rank in the Boy Scouts of America, above tenderfoot and second class, that traditionally has required proficiency in scoutcraft skills.