IPA: /ˈfiːblnəs/
KK: /ˈfiblnəs/
The condition of being weak or lacking strength, often due to illness or age.
His feebleness made it difficult for him to climb the stairs.
Feebleness is formed from "feeble" (from Old French *feeble*, meaning weak) and the suffix "-ness" (meaning the state or quality of). The word "feebleness" refers to the state of being weak or lacking strength.
Think of 'feeble' meaning weak, and remember that 'feebleness' describes the state of being weak.