IPA: /əˈmjuːzɪŋnəs/
KK: /əˈmyuzɪŋnəs/
The quality of being funny or entertaining.
The amusingness of the comedian's jokes kept the audience laughing throughout the show.
Amusingness is formed from "amuse" (from Old French *amuser*, meaning to divert or entertain) and "-ness" (meaning the state or quality of). The word "amusingness" refers to the quality of being entertaining or diverting.
Think of the word 'amuse' which means to entertain, and remember that 'amusingness' is the quality of being entertaining.