The Greek adjective asthenes (ἀσθενής) means "weak, feeble, sick, powerless" — from the alpha-privative a- and sthenos (strength). It encompasses both physical weakness/illness and moral or spiritual weakness. In the New Testament it is used extensively in all these dimensions.
Paul's theology of weakness, centered on asthenes, is one of the most distinctive features of his apostolic self-understanding. In 1 Corinthians 1:27, God chooses the weak (asthene) things of the world to shame the strong. In 2 Corinthians 12, Paul glories in his weaknesses because "when I am weak, then I am strong" — Christ's power is perfected in human insufficiency. Romans 5:6 declares that "Christ died for the ungodly... when we were still powerless (asthenes)." The sick person (asthenes) in James 5:14 is to call the elders for prayer and anointing — a pastoral provision for physical weakness. Christ himself was "crucified in weakness" (2 Corinthians 13:4) yet raised in power.