The concept of sin is developed through a variety of Hebrew terms that describe various aspects of it. When used in the context of a contrast to God's character and word, one Hebrew noun in particular stands out.

Ra' (Strong's #H7451)

This masculine noun means evil, bad, or contrary to God's nature.

God introduces the term as a contrast to good and associated with death.

The Lord God commanded the man, saying, "From any tree of the garden you may eat freely; but from the tree of the knowledge of good and evil (ra') you shall not eat, for in the day that you eat from it you will surely die." (Gen 2:16-17)

God clearly indicates that by eating the forbidden fruit, Adam and Eve received some level of moral knowledge; thus, their sinful action enabled them to discern good from evil before the Mosaic Law was introduced. This also means that human beings were capable of discerning right from wrong when Jesus Christ makes the appeal to repent and believe.

Then the Lord God said, "Behold, the man has become like one of Us, knowing good and evil (ra'); and now, he might stretch out his hand, and take also from the tree of life, and eat, and live forever" (Gen 3:22)

Then the Lord saw that the wickedness (ra') of man was great on the earth, and that every intent of the thoughts of his heart was only evil (ra') continually. (Gen 6:5)

God clearly links evil to disobedience of God's word and unworthy sacrifices for atonement. This provides context to the sacrifice of His only Son Jesus Christ for the atonement of mankind's sin.

"You shall not sacrifice to the LORD your God an ox or a sheep which has a blemish or any defect (ra'), for that is a detestable thing to the LORD your God. If there is found in your midst, in any of your towns, which the LORD your God is giving you, a man or a woman who does what is evil (ra') in the sight of the LORD your God, by transgressing His covenant, (Deut 17:1-2)

Then the sons of Israel did evil (ra') in the sight of the Lord and served the Baals, and they forsook the Lord, the God of their fathers, who had brought them out of the land of Egypt, and followed other gods from among the gods of the peoples who were around them, and bowed themselves down to them; thus they provoked the Lord to anger. (Judg 2:11-12)

When the Old Testament was translated into Greek (LXX), Jewish scholars translated the Hebrew ra' predominantly into Greek as "kakŏs." However in the New Testament, "kakŏs," and its associated word group, was not the primary Greek term used for evil.

Kakŏs (Strong's #G2556)

When used in the context of sin, this adjective means "morally bad or evil that threatens one's existence." It is often used as a contrast to good.

Jesus speaks of the propensity to sin as a reflection of one's heart, and He used kakŏs to describe the thoughts of a sinner that leads to immoral behavior.

And He was saying, "That which proceeds out of the man, that is what defiles the man. For from within, out of the heart of men, proceed the evil (kakŏs) thoughts, fornications, thefts, murders, adulteries, deeds of coveting and wickedness, as well as deceit, sensuality, envy, slander, pride and foolishness. All these evil things proceed from within and defile the man." (Mark 7:20-23)

In speaking about the purpose of the Law, the apostle Paul reveals that knowledge of the Law tempted his sin nature to rebel against the word of God (Rom 7:7-8).

For the good that I want, I do not do, but I practice the very evil (kakŏs) that I do not want. But if I am doing the very thing I do not want, I am no longer the one doing it, but sin which dwells in me. I find then the principle that evil (kakŏs) is present in me, the one who wants to do good. (Rom 7:19-21)

While one may not understand the nature of sin, it is associated with easily recognizable behavioral characteristics. When there is no love for God, sin prevails.

Do not be deceived: "Bad (kakŏs) company corrupts good morals." (1 Cor 15:33)

For the love of money is a root of all sorts of evil (kakŏs), and some by longing for it have wandered away from the faith and pierced themselves with many griefs. (1 Tim 6:10)

Sin and evil are total opposites to agapē which is God's form of love.

Love (agapē) does no wrong (kakŏs) to a neighbor; therefore love is the fulfillment of the law. (Rom 13:10)

Throughout the New Testament, the most common Greek term for evil is pŏnērŏs.

Pŏnērŏs (Strong's #G4190)

This Greek adjective means "in poor condition, evil, or bad;" when used in the context of a person, there is an emphasis on "evil, depraved, or corrupt" and ethically as opposed to God.

Evil comes from a man's heart in the form of evil thoughts. Here there is the idea that sin originates from the heart.

You brood of vipers, how can you, being evil (pŏnērŏs), speak what is good? For the mouth speaks out of that which fills the heart. The good man brings out of his good treasure what is good; and the evil (pŏnērŏs) man brings out of his evil (pŏnērŏs) treasure what is evil (pŏnērŏs). (Matt 12:34-35)

All these evil (pŏnērŏs) things (pŏnērŏs) proceed from within and defile the man." (Mark 7:23)

Take care, brethren, that there not be in any one of you an evil (pŏnērŏs), unbelieving heart that falls away from the living God. (Heb 3:12)

Evil thoughts are expressed in sinful behaviors.

And although you were formerly alienated and hostile in mind, engaged in evil (pŏnērŏs) deeds, yet He has now reconciled you in His fleshly body through death, in order to present you before Him holy and blameless and beyond reproach (Col 1:21-22)

So every good tree bears good fruit, but the bad tree bears bad (pŏnērŏs) fruit. A good tree cannot produce bad (pŏnērŏs) fruit, nor can a bad tree produce good fruit. (Matt 7:17-18)

When pŏnērŏs is contrasted with good, one is presented with two choices of living and whom they serve, consciously or not. Those who are with sin that has not been not been atoned for are judged as unrighteous.

But if your eye is bad (pŏnērŏs), your whole body will be full of darkness. If then the light that is in you is darkness, how great is the darkness! No one can serve two masters; for either he will hate the one and love the other, or he will be devoted to one and despise the other. You cannot serve God and wealth. (Matt 6:23-24)

And He said, "The one who sows the good seed is the Son of Man, and the field is the world; and as for the good seed, these are the sons of the kingdom; and the tares are the sons of the evil (pŏnērŏs) one; and the enemy who sowed them is the devil, and the harvest is the end of the age; and the reapers are angels. (Matt 13:37-39)

While sin, including unintentional ones, is characterized as being evil to express anything against God, pŏnērŏs is also used to describe sin as "wicked" which can be understood as a greater degree of evil - an intentional sin against another being in which the offender is unashamed and feels no guilt.

So it will be at the end of the age; the angels will come forth and take out the wicked (pŏnērŏs) from among the righteous, and will throw them into the furnace of fire; in that place there will be weeping and gnashing of teeth. (Matt 13:49)

Jesus is referring to the end of human history when, after all Believers have died or been martyred, His angels are reaping the earth (Rev 14:18-20).

For this is the message which you have heard from the beginning, that we should love (agapeō) one another; not as Cain, who was of the evil (pŏnērŏs) one (pŏnērŏs) and slew his brother. And for what reason did he slay him? Because his deeds were evil (pŏnērŏs), and his brother's were righteous. (1 John 3:11-12)

While translators did not use the English term "wicked" in this passage, Cain's murderous act clearly associates him with Satan (i.e. "of the pŏnērŏs one"), and he lies and responds with distain to God's question (Gen 4:9). This is in sharp contrast to his parents' response to their sin; they lied but were ashamed (Gen 3:8-12).