- Decrepit implies a being broken down, worn out, or decayed, as by old age or long use a decrepit old pensioner, a decrepit sofa
- Infirm suggests a loss of strength or soundness, as through illness or age his infirm old grandfather
- Frail suggests an inherent or constitutional delicacy or weakness, so as to be easily broken or shattered a frail body, conscience, etc.
- Feeble suggests a pitiable weakness or ineffectiveness a feeble old man, a feeble joke
- Weak , the broadest in application of these words, basically implies a lack or inferiority of physical, mental, or moral strength a weak muscle, mind, character, foundation, excuse, etc.