A-flat

noun3

1. •
   A tone one semitone below A, between G and A, denoted A♭.

   • The bassoon came in on a low A-flat.
2. •
   The key of A-flat major.

   • We will now hear the third sonata, in A-flat.
3. •
   A key or other mechanism for producing an A-flat.

   • I had to take it to the shop because the A-flat was stuck.