A1 A1 /eɪ wʌn/

adjective

1. [Informal] Of the highest quality, skill, etc.; very good or impressive  ( A1 [Informal] , beezer [Archaic, UK] , shit-hot [Vulgar] , top-drawer )
   of the highest quality, skill, etc.; very good or impressive
    An ace reporter
   an ace reporter
    A crack shot
   a crack shot
    Made an excellent speech
   made an excellent speech
   

noun

1. Paper size, 594 x 841 mm.  ( A1 )
   Paper size, 594 x 841 mm.