IMPROVISE v. 2 definitions
To compose, recite, or sing extemporaneously, especially in verse; to extemporize; also, to play upon an instrument, or to act, extemporaneously.
KEY n.
or four, submediant or six, supertonic or two, and subtonic or seven. Chromatic tones are temporary members of a key, under such names as " sharp four," "flat seven," etc. Scales and tunes of every variety are made from the tones of a key.