a1

Short definition from Wiktionary

Adjective

1. 1
   first rate or excellent
2. 2
   in first class condition
3. 3
   In good health.
4. 4
   In excellent or top condition.
5. 5
   First-class. (Compare A 2 and A 3, which are inferior grades.)

Noun

1. 1
   Under the International Union of Railways (French: Union internationale des chemins de fer, UIC) classification system, a steam locomotive that has two coupled driving wheels followed by two trailing wheels, with no leading wheels; also called an 0-2-2.