“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.
“Again, the kingdom of heaven is like a merchant seeking beautiful pearls, who, when he had found one pearl of great price, went and sold all that he had and bought it.” Matthew 13:45-46.