Tonic
The note upon which a scale or key is based; the first note of a scale or key; the keynote.
Note
A notational symbol used to represent the duration of a sound, and when placed on a music staff, also indicate the pitch of the sound.
Scale
A series of notes in ascending or descending order that presents the pitches of a key or mode, beginning and ending on the tonic of that key or mode. The degrees of a scale have specific names shown below -- and each of the unique 12 notes of the chromatic scale can be the tonic note of a scale.
1 - Tonic
2 - Supertonic
3 - Mediant
4 - Subdominant
5 - Dominant
6 - Submediant or Superdominant
7 - Leading Note or Subtonic
Key
A specific scale or series of notes defining a particular tonality. Keys may be defined as major or minor, and are named after their tonic or keynote. Thus the series of notes with intervals defining a major tonality and based on the key of C is the key of C major.
Keynote
The note upon which a scale or mode is based or around which a composition is centered.