IPA: /ˈtjuːn.fəl.nəs/
KK: /ˈtjunfəl/
The quality of being pleasant to listen to, especially in music or singing.
The tunefulness of the choir filled the hall with beautiful sounds.
Tunefulness → It is formed from "tune" (from Old French *ton*, meaning a musical sound or melody) and "-ful" (meaning full of) and "-ness" (meaning the state of being). The word "tunefulness" means the state of being full of melody or musical sound.
Think of 'tune' as a musical sound, and remember that 'tunefulness' means being full of that musical quality.