The Collaborative International Dictionary of English v.0.48:

First-class \First"-class`\, a.
   Of the best class; of the highest rank; in the first
   division; of the best quality; first-rate; as, a first-class
   telescope.
   [1913 Webster]

   First-class car or First-class railway carriage, any
      passenger car of the highest regular class, and intended
      for passengers who pay the highest regular rate; --
      distinguished from a second-class car.
      [1913 Webster]

WordNet (r) 3.0 (2006):

first-class
    adj 1: very good;of the highest quality; "made an excellent
           speech"; "the school has excellent teachers"; "a first-
           class mind" [syn: excellent, first-class,
           fantabulous, splendid]