Definition of Iniquity
As found in the Bible, “iniquity” is defined as being wicked or immoral in nature or character. Primarily, it indicates "not an action, but the character of an action", and is so distinguished from "sin". Therefore, we have the phrase "the iniquity of my sin" (Psalms 32:5). Iniquity can be described as the essence of wrongdoing or evil, while sin is this quality actually enacted in the world.
Merriam-Webster provides further context for the meaning of iniquity as used in the following sentence: “The use of illegal narcotics is not only a destroyer of personal health but also an iniquity that undermines our society.”
Synonyms of Iniquity: corruption, degeneracy, immorality, sin, vice.
Iniquity in the Bible
The soul who sins shall die. The son shall not suffer for the iniquity of the father, nor the father suffer for the iniquity of the son. The righteousness of the righteous shall be upon himself, and the wickedness of the wicked shall be upon himself. Ezekiel 18:20
Keeping steadfast love for thousands, forgiving iniquity and transgression and sin, but who will by no means clear the guilty, visiting the iniquity of the fathers on the children and the children's children, to the third and the fourth generation.” Exodus 34:7
And no longer shall each one teach his neighbor and each his brother, saying, ‘Know the Lord,’ for they shall all know me, from the least of them to the greatest, declares the Lord. For I will forgive their iniquity, and I will remember their sin no more.” Jeremiah 31:34
The Difference between Iniquity, Sin, and Transgression
There are three primary Hebrew words which are often used correspondently. These words are often translated as sin, iniquity, or transgression. Chattah, which is most often translated as sin, means to miss the mark. Awon, often translated as iniquity, relates more to the inner character and points to an intentional twisting of a given standard. Pesha, often translated as transgression, is more of a willful rebellion against the given standard. We see these words in their nuances and also used interchangeably in Psalm 51:
Have mercy on me, O God, according to your steadfast love; according to your abundant mercy blot out my pesha [transgressions]. Wash me thoroughly from my awon [iniquity], and cleanse me from my chattah [sin]! For I know my pasha [transgressions], and my chattah [sin] is always before me. Against you, you only, have I chattah [sinned] and done what is evil in your sight, so that you may be justified in your words and blameless in your judgment. Behold, I was brought forth in awon [iniquity] and in chattah [sin]did my mother conceive me.
In Psalm 32:5, the psalmist says, “I acknowledged my sin to you and did not cover up my iniquity. I said, ‘I will confess my transgressions to the LORD.’” In this one verse, “sin,” “iniquity,” and “transgression” are all mentioned. Basically, the three words communicate the same idea: evil and lawlessness, as defined by God (1 John 3:4). Though, upon closer inspection, each word also bears a somewhat separate meaning.
Meaning of Sin
Sin signifies “to miss the mark.” It can indicate doing something against God or against a person (Exodus 10:16), doing the contrast of what is right (Galatians 5:17), doing something that will have adverse results (Proverbs 24:33–34), and neglecting to do something you know is right (James 4:17). In the Old Testament, God even established sacrifices for unintentional sins (Numbers 15:27). Sin is the common phrase for anything that “falls short of the glory of God” (Romans 3:23).
Meaning of Iniquity
Iniquity indicates a conscious decision; to commit iniquity is to proceed without repentance. Micah 2:1 says, “Woe to those who plan iniquity, to those who plot evil on their beds! At morning’s light, they carry it out because it is in their power to do it.” In David’s psalm of repentance, he cries out to God, saying, “Wash away all my iniquity and cleanse me from my sin” (Psalm 51:2).
God forgives iniquity, as He does any sort of sin when we genuinely repent (Hebrews 8:12). However, iniquity left unchecked advances to a point of intentional sin with no fear of God. The growth of shameless sin is sometimes portrayed as a “cup of iniquity” being filled to the brim (Revelation 17:4). This often pertains to nations who have forsaken God entirely. Continued iniquity leads to irregular desires, which leads to a degenerate mind. Romans 1:28-32 describes this deviation in graphic detail. The sons of Eli are biblical examples of sinners whom God judged for their iniquities. Rather than repent, Eli’s sons continued in their evils until remorse was no longer possible.
Merriam-Webster | Iniquity
Crosswalk.com | What Are Iniquities and How Are They Different Than Our Sins?
Gotquestions.org | What is the difference between iniquity, sin, and transgression?