Source : Webster's Revised Unabridged Dictionary (1913)

Osteoporosis \Os`te*o*po*ro"sis\, n. [NL.; osteo- + Gr. ? pore.]
   (Med. & Physiol.)
   An absorption of bone so that the tissue becomes unusually
   porous.

Source : WordNet®

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