flac-cid / flăs-ĭd, flăk-sĭd
1. flabby; hanging loosely; not firm
The nerve of the savage had gone, and his muscle had become a flaccid thing.
From “A Millionaire of Yesterday” by E. Phillips Oppenheim, 1866 – 1946
2. weak; lacking force, vigor or endurance
But the Roman Empire, in its feeble and flaccid old age, seemed to have lost all capacity for making war.
From “Theodoric the Goth” by Thomas Hodgkin, 1831 – 1913
Either through the French adjective flaccide (loose, flabby) or directly from the Latin adjective flaccidus, flaccida, flaccidum of the same meaning. It is derived from a combination of the Latin adjective-forming suffix -idus, -ida, -idum and the Latin verb flacceo, flaccere, ___, ___ (be flabby, droop, wilt), which seems to have been back-formed from the Latin adjective flaccus, flacca, flaccum (flabby, flap-eared) of uncertain origin.
Thank you to Allen Ward for providing this etymology.