The quality or state of being frothy; the presence of froth, foam, or bubbles, or the characteristic of being insubstantial or frivolous.
From 'frothy' plus the noun suffix '-ness,' which converts adjectives to abstract nouns describing qualities or states.
The suffix '-ness' is incredibly productive in English—you can theoretically add it to almost any adjective to create a noun, which gives English speakers creative flexibility in describing qualities.
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