These adjectives mean lacking or showing a lack of strength. Weak is the most widely applicable: “These poor wretches … were so weak they could hardly sit to their oars” (Daniel Defoe). Feeble suggests pathetic or grievous physical or mental weakness or hopeless inadequacy: a feeble intellect; a feeble effort.Frail implies delicacy and inability to endure or withstand: “an aged thrush, frail, gaunt, and small“ (Thomas Hardy.) What is fragile is easily broken, damaged, or destroyed: a fragile, expensive vase; a fragile state of mind after the accident.Infirm implies enfeeblement: “a poor, infirm, weak, and despis'd old man” (Shakespeare). Decrepit describes what is weakened, worn out, or broken down by hard use or the passage of time: a decrepit building slated for demolition.Debilitated suggests a gradual impairment of energy or strength: a debilitated constitution further weakened by overwork.