Definition of "debility"

As I was in a state of extreme debility, I resolved to sail directly towards the town, as a place where I could most easily procure nourishment. […] I was ready to sink from fatigue and hunger, but being surrounded by a crowd, I thought it politic to rouse all my strength, that no physical debility might be construed into apprehension or conscious guilt.

1818, [Mary Shelley], Frankenstein; or, The Modern Prometheus. […], volumes (please specify |volume=I to III), London: […] [Macdonald and Son] for Lackington, Hughes, Harding, Mavor, & Jones

I was struck besides with the shocking expression of his face, with his remarkable combination of great muscular activity and great apparent debility of constitution

1886, Robert Louis Stephenson, The Strange Case of Dr Jekyll and Mr Hyde