A-one

First-class; excellent.

[From classification for ships in The Lloyd's Register of Shipping.]

adjective

Exceptionally good of its kind: ace, banner, blue-ribbon, brag, capital, champion, excellent, fine, first-class, first-rate, prime, quality, splendid, superb, superior, terrific, tiptop, top. Informal bully, dandy, great, swell, topflight, topnotch. Slang boss. Chiefly British tophole. See good/bad.

Also, A-1; ; A-number-one. First-class, of the best quality, as in This is an A-one steak. The term comes from Lloyd's, the British insurance company, which in its 1775 shipping register designated the condition of a ship's hull by a letter grade (A, B, etc.) and of its cables, anchor, and other equipment by a number grade (1, 2, etc.). By the early 1800s A-1, the best possible grade, was being transferred to anything of superior quality.

The adjective has one meaning:

Meaning #1: (informal) of the highest quality
  Synonyms: ace, crack, first-rate, super, tiptop, topnotch, tops