The characteristic or quality of being flabby(noun)
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Use "flabbiness" in a sentence
"He did not know that what he called her flabbiness was the inertia in which they stored their strength, nor that in them there remained a vigilant and indestructible soul, biding its time, holding its own against maternity, making more and more for self-protection, for assertion, for supremacy."
"We may thrill with dread at the aggressive hyphenate, but this tame flabbiness is accepted as Americanization."
"Page 36 men "with a direct view to gaining a livelihood;" Barrett Wendell wrote in the North American Review in 1904 on "Our National Superstition" in which he pointed to the "flabbiness" of college students."