Noun

1. A tone four fifths below C in the cycle of fifths, intermediate between G and A, denoted A♭.

   The bassoon came in on a low A-flat.

2. A key or other mechanism for producing an A-flat.

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

3. The key of A-flat major.

   We will now hear the third sonata, in A-flat.