This word comes directly from Greek into English, letter-for-letter: hades.
W.E. Vine noted that some derive the term from the negative prefix a ("not") and eido ("seen"), hence "the unseen," though he considered it more likely that it comes from hado, signifying "all receiving."
In the King James Version, hades is rendered "hell," but this is incorrect. Hades is the generic word for the intermediate state of the dead (i.e., the receptacle of the soul). This would be the same post-death environment, whether pertaining to the righteous or the wicked. Jesus was in Hades while his body lay in the tomb (Acts 2:27). Likewise, the selfish rich man mentioned by Christ was tormented in his Hadean abode (Lk. 16:23).
At the time of Christ's return, all bodies will be raised from the dead (Jn. 5:28-29; Acts 24:15). At the same time, Hades will surrender the spirits it has retained (Rev. 1:18; 20:13-14). Then, both the good people and the bad will enter their final destinies, with bodies (incorruptible in nature — 1 Cor. 15:53-54) and souls reunited (Mt. 10:28; 2 Cor. 5:1ff).