The Collaborative International Dictionary of English v.0.48:
frailness \frail"ness\, n. Frailty. [1913 Webster]WordNet (r) 3.0 (2006):
frailness n 1: the state of being weak in health or body (especially from old age) [syn: infirmity, frailty, debility, feebleness, frailness, valetudinarianism]