From The Collaborative International Dictionary of English v.0.48:
resilience \re*sil"i*ence\ (r[-e]*z[i^]l"[i^]*ens), resiliency
\re*sil"i*en*cy\ (r[-e]*z[i^]l"[i^]*en*s[y^]), n.
1. The act of springing back, rebounding, or resiling; as,
the resilience of a ball or of sound.
[1913 Webster]
2. The power or inherent property of returning to the form
from which a substance is bent, stretched, compressed, or
twisted; elasticity[1]; springiness; -- of objects and
substances.
[PJC]
3. Hence: The power or ability to recover quickly from a
setback, depression, illness, overwork or other adversity;
buoyancy; elasticity[2]; -- of people.
[PJC]
4. (Mech. & Engin.) The mechanical work required to strain an
elastic body, as a deflected beam, stretched spring, etc.,
to the elastic limit; also, the work performed by the body
in recovering from such strain.
[1913 Webster]