The quality of being soapy or having the characteristics of soap.
Saponaceousnesses is usually a good thing because it means something is clean or has the properties of soap.
Examples:
The saponaceousnesses of the water made it perfect for washing.
I like the saponaceousnesses of this soap.
The saponaceousnesses of the bubbles made them last a long time.
The saponaceousnesses of the floor made it very slippery.
The saponaceousnesses of this shampoo makes my hair extra clean.
The saponaceousnesses of the detergent was so strong, it cleaned everything.