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Of the very highest caliber, standard, or quality. That was a positively A1 performance last night.
A-1and A number 1
mod. of the highest rating. This steak is really A-1!
The best quality. The term originated in the 1775 edition of Lloyd’s Register of British and Foreign Shipping, in which the state of a ship’s hull was designated by a letter grade and the condition of the anchor, cables, and so forth by a number grade. This insurance rating was soon transferred to numerous other areas and has been a cliché since the late nineteenth century.