1. Weak, lax and soft. (biology-online.org)
2. Out of condition; not strong or robust; incapable of exertion or endurance. (wordnetweb.princeton.edu)
3. Soft and hanging loosely or limply, esp. so as to look or feel unpleasant. (Google Dictionary)
4. Drooping without elasticity; wanting in stiffness. (wordnetweb.princeton.edu)
a. Drooping or inelastic through lack of water. (Google Dictionary)
Word origin: Latin flaccidus.