The adjectival form of the noun 'frailty' is frail.
Achilles heel*, blemish, daintiness, debility, decrepitude, defect, deficiency, delicacy, error, failing, fallibility, fault, feebleness, flimsiness, foible, foil, imperfection, infirmity,...
yes and no it can be used in any way
Fragile.
admiralty