osteoporosis
    n 1: abnormal loss of bony tissue resulting in fragile porous
         bones attributable to a lack of calcium; most common in
         postmenopausal women

Osteoporosis \Os`te*o*po*ro"sis\, n. [NL.; osteo- + Gr. po`ros
   pore.] (Med. & Physiol.)
   An absorption of bone so that the bone tissue becomes
   unusually porous. It occurs especially in elderly men and
   postmenopausal women, and predisposes the elderly to
   fractures of the bones.
   [Webster 1913 Suppl. +PJC]