Frailty describes a quality that's shared by a sick kitten, an elderly man, and a shoddily built go cart. They all have a delicate weakness or vulnerability and seem to require some kind of care.
The Old French fraileté, or "weakness" is the root of frailty, and it in turn comes from the Latin word for "fragile," fragilis. What's interesting is that "fragility" was used in the 14th century to mean a kind of moral, rather than physical, weakness. Today frailty can be used this way too, to describe a state of having shaky — or fragile — morals.
