When we read in the Bible the word “sick”, it is easy to mistake it for one and the same word…all having the same meaning. The three verses below all have the word “sick” and each one is a different word in the Greek and each one has a very different meaning.
Verse: James5.13 Is anyone among you suffering? Let him pray. Is anyone cheerful? Let him sing praise. 14 Is anyone among you sick? Let him call for the elders of the church, and let them pray over him, anointing him with oil in the name of the Lord. 15 And the prayer of faith will save the one who is sick, and the Lord will raise him up. And if he has committed sins, he will be forgiven. 16 Therefore, confess your sins to one another and pray for one another, that you may be healed. The prayer of a righteous person has great power as it is working.
Definition: [Sick]: Primarily to work, be weary from constant work (Heb. 12:3; Job 10:1), to be sick, it suggests the common accompaniment of sickness, weariness of mind which may hinder physical recovery (James 5:15).
Application This is a well-known verse that is misunderstood. There is a different understanding waiting for us and this understanding gives us a new insight. Actually the word here means weariness and this weariness is causing the sickness. So we need to actually pray for the root of the weariness and once the weariness is relieved there will be recovery.
Verse: Acts5.15 so that they even carried out the sick into the streets and laid them on cots and mats, that as Peter came by at least his shadow might fall on some of them. 16 The people also gathered from the towns around Jerusalem, bringing the sick and those afflicted with unclean spirits, and they were all healed.
Definition: [Sick] without, strength. Without strength, powerless; Weak, powerless, without physical ability (Matt. 26:41, “the flesh is weak,” impotent, i.e., unequal to the task; Mark 14:38; 1 Pet. 3:7; Sept.: Num. 13:19; Job 4:3; Ezek. 17:14). Including the idea of imperfection (1 Cor. 12:22; Gal. 4:9; Heb. 7:18). In 1 Cor. 1:25 as a subst., “the weakness of God” means the weak but godly person; in 1 Cor. 1:27 “the weak things of the world,” spoken of men who are naturally weak. Infirm, sick, sickly, diseased (Matt. 25:39, 43, 44; Luke 10:9; Acts 4:9; 5:15, 16; 1 Cor. 11:30); without strength or weak in a spiritual sense, weak with regard to spiritual things (2 Cor. 10:10 [cf. 1 Cor. 2:3; 2 Cor. 11:21]). Implying a want of decision and firmness of mind, weak–minded, i.e., doubting, hesitating, vacillating in opinion or in faith (1 Cor. 8:7, 10; 9:22; 1 Thess. 5:14). By implication, meaning afflicted, distressed by oppression, calamity, and so forth (1 Cor. 4:10
Application: Here in Acts it is a sickness that means weakness in body and in spirit.
Verse: Luke7.2 Now a centurion had a servant who was sick and at the point of death, who was highly valued by him.
Definition: [Sick] Meaning to have it badly. Physically: to be ill (Matt. 4:24; 8:16; 9:12; 14:35; Mark 1:32, 34; 2:17; 6:55; Luke 5:31; 7:2), to suffer badly, i.e., grievously (Matt. 17:15). 
Application: Here in Luke it is used as we would normally think of the word sick…physically ill.
 Zodhiates, S. (2000). The complete word study dictionary : New Testament (electronic ed.). Chattanooga, TN: AMG Publishers.
Published on Friday, July 8, 2011 @ 5:03 AM CDT