“Beware, brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; but exhort [encourage] one another daily, while it is called ‘Today,’ lest any of you be hardened through the deceitfulness of sin.” Hebrews 3:12-13.
The dictionary defines evil as, morally wrong; immoral; wicked. It could be something harmful or injurious; the synonyms though may be the best descriptions.
Depending on how it is used evil can be; sinful, iniquitous, depraved, base, vile, nefarious, pernicious, destructive, wickedness, unrighteousness, or corruption, to name a few.
“A worthless person, a wicked man, walks with a perverse mouth [fraudulent deceitful speech]; he winks with his eyes, he shuffles his feet, he points with his fingers; perversity is in his heart, he devises evil continually, he sows discord. Therefore his calamity shall come suddenly; suddenly he shall be broken without remedy.” Proverbs 6:12-15.
“These six things the Lord hates, yes, seven are an abomination to Him: a proud look, a lying tongue, hands that shed innocent blood, a heart that devises wicked plans, feet that are swift in running to evil, a false witness who speaks lies, and one who sows discord among brethren.” Proverbs 6:16-19.
“O Lord, our Lord, how excellent is Your name in all the earth, You who set Your glory above the heavens! Out of the mouths of babes and nursing infants You have ordained strength, because of Your enemies, that You may silence the enemy and the avenger.” Psalm 8:1-2.
“…who [Jesus, God the Son], being in the form of God, did not consider it robbery to be equal with God, but made Himself of no reputation, taking the form of a bondservant, and coming in the likeness of men. And being found in appearance as a man, He humbled Himself and became obedient to the point of death, even the death of the cross. Therefore God also has highly exalted Him and given Him the name which is above every name, that at the name of Jesus every knee should bow, of those in heaven, and of those on earth, and of those under the earth, and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.” Philippians 2:6-11.