NOUN (3)

1. the state of being vigorous and robust;

2. the property of something that is strongly built;

3. resoluteness evidenced by strength of character;
- Example: "sturdiness of moral principle"

The Collaborative International Dictionary of English v.0.48:

Sturdiness \Stur"di*ness\, n.
   Quality of being sturdy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sturdiness
    n 1: the state of being vigorous and robust
    2: the property of something that is strongly built
    3: resoluteness evidenced by strength of character; "sturdiness
       of moral principle"