A-one also A-1 (??w?n?)adj. Informal First-class; excellent.[From classification for ships in The Lloyd’s Register of Shipping.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.A one or A 1 (?e? ?w?n) adj. 1. first-class; excellent. 2. (of a ship) maintained in first-class condition. [1830?40] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.