This is an excellent question, for some are inclined to think they all mean the same thing. There are differences, even though they are closely related at times. We will take up each one by quoting verses, followed by a definition and a few comments.

1) In Psalm 51:5 we read, “Behold, I was brought forth in iniquity, and in SIN my mother conceived me.” In Romans 3:23 we read, “For all have SINNED and fall short of the glory of God.” The word “sin” literally means “a missing of the mark.” Just as one may try to hit the bull’s eye on a target with a bow and arrow consistently and yet fail at times, so the “sinner” will fail to reach God’s perfect standard of righteousness at times. We were all “born in SIN” (we inherited a SIN NATURE from our human parents who are sinners…. John 3:6 with Romans 7:18-20). And until we are born again, we all “practice SIN.” There is a clear definition of SIN in 1 John 3:4, “Everyone who PRACTICES SIN also PRACTICES LAWLESSNESS; and SIN IS LAWLESSNESS” (NASB). The KJV here says, “SIN is the transgression of the law,” but as we shall see when we look at the word “transgression,” sin is not limited to “breaking one of God’s commandments: SIN is refusing to acknowledge God in our life for we want to “have our own way” instead of “God having His way in our life.” Isaiah 53:6 speaks to this, “All we like sheep have gone astray; we have turned everyone to HIS OWN WAY.

2)  In Matthew 7:23 and 13:41 we read, “And then I will profess unto them, I never knew you: depart from me, ye that work INIQUITY…The Son of Man shall send forth his angels, and they shall gather out of his kingdom all things that offend, and them which do INIQUITY” (KJV). The word literally means, “unrighteousness” which is “doing what is WRONG instead of doing what is RIGHT.” It is interesting to note that in other translations this word (in these two verses) is translated “lawlessness.” We already saw that “SIN is LAWLESSNESS” so these the words SIN and INIQUITY are very close in meaning. This is borne out in Isaiah 53:5-6, “But He was wounded for our transgressions, He was bruised for our INIQUITIES…the LORD has laid on Him the INIQUITY of us all.” We know from 1 Peter 2:24 that it was indeed our SINS that were laid on Him, “Who Himself bore our SINS in His own body on the tree.”

3) We just saw the word TRANSGRESSIONS in Isaiah 53:5, “He was wounded for our TRANSGRESSIONS.” Since that is followed by Jesus being “bruised for our INIQUITIES’ there must be a difference between them. The word “transgression” literally means, “to go beyond.” The question is, “To go beyond what?” It is to “go beyond God’s written commandments.” This is confirmed in the words of Jesus in Matthew 15:3, “Why do you also TRANSGRESS the commandment of God because of your tradition?” We saw that the KJV rendering of 1 John 3:4 is, “SIN is the TRANSGRESSION of the law,” but we noted that sin is not limited to “breaking a certain commandment.” This is seen clearly in Romans 5:13-14, “For until the law SIN WAS IN THE WORLD, but sin is not imputed when there is no law. Nevertheless death reigned from Adam to Moses, even over those who had not sinned according to the likeness of the TRANSGRESSION of Adam.” Adam had been given a direct commandment (Genesis 2:15-17) and when he “broke that commandment” he had committed a TRANSGRESSION. No one had been given any commandments between Adam and Moses yet “sin was in the world.”

4) In Ephesians 2:1 we read, “And you He made alive, who were dead in TRESPASSES and sins.” This verse teaches us there is an obvious difference between a “trespass” and a “sin.” The word “trespass” means “a false step, to fall away.” It is very close in meaning to “transgression” for it implies breaking a known law. For example, if you see a sign saying, “No TRESPASSING,” you know you can’t “go beyond that sign.” We saw that when Adam broke God’s commandment he was guilty of a “transgression,” but his disobedience was also a “false step”; it led to “his fall” and to the “fall of man.” He had TRESPASSED by going up to the tree of the knowledge of good and evil and eating the forbidden fruit. His TRESPASS is referred to in Romans 5:15-17, “But the free gift is not like the TRESPASS. For many died through one man’s TRESPASS….For the judgment following one TRESPASS brought condemnation….Because of one man’s TRESPASS, death reigned through that one man” (RSV). Again, Adam was guilty of a “false step” which resulted in “his fall and the fall of man (the whole human race).”  (DO)  (625.5)