Dake’s Annotated Reference Bible (with some changes): Death defined: The word death as applied to man in Scripture means the separation or a cutting off from realizing God’s purpose for which man was created [Gen 2:15]. One can logically substitute the word separation for death in every scripture where it is used.
Physical death is theseparationof the inner man from the outer man; the separation of the soul and spirit from the body.
(Gen 3:19) In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken: for dust thou art, and unto dust shalt thou return.
(Eccl 12:7) Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it.
Spiritual death is theseparationof man from God because of sin. A person spiritually dead can be alive physically, or he can be dead physically and alive in hell, conscious in the untransformed soul (Rom 12:2) of the inner man.
(Mat 8:22) But Jesus said unto him, Follow me [and live]; and let the dead bury their dead.
(1 Tim 5:5,6) Now she that is a widow indeed, and desolate, trusteth in God, and continueth in supplications and prayers night and day. But she that liveth in pleasure is dead while she liveth.
Eternal death iseternal separation from God because man chooses to remain[a questionable Arminian phrase that may be rephrased into Calvinism to “remains”] separated from God in sin.
(Mat 25:41) Then shall he say also unto them [the goats]on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:
(Mat 25:46) And these [goats on the left hand] shall go away into everlasting punishment: but the righteous [sheep on the right hand] into life eternal.
(Isa 66:22-24) For as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain. And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD. And they shall go forth, and look upon the carcases[corpses, dead bodies]of the men that have transgressed against me: for their worm shall not die, neither shall their fire be quenched; and they shall be an abhorring unto all flesh.
(Mark 9:43-48) And if thy hand offend thee, cut it off: it is better for thee to enter into life maimed, than having two hands to go into hell, into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feet to be cast into hell, into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thine eye offend thee, pluck it out: it is better for thee to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire: Where their worm dieth not, and the fire is not quenched.