Synonyms for Flaccid (same or very similar meaning)
WordNet sense 1 (lacking in strength or firmness or resilience):
lax, limp, slackWordNet sense 2 (having little physical or spiritual strength):
weakWordNet sense 3 (yielding readily to pressure or weight):
softWordNet sense 4 (out of condition; not strong or robust; incapable of exertion or endurance):
flabbyWordNet sense 5 (not in good physical or mental condition; out of condition):
unfitFrom the ODE community, based on WordNetadd/edit