dead: having died, no longer alive; used as a noun for dead persons, and above all in the phrase "from the dead" as the fixed idiom for resurrection.
The word's basic force is simply the absence of physical life. It names a state (dead, not alive) or the people who are in that state (the dead). In both roles it appears throughout the Gospels, Acts, and the letters with unremarkable plainness: a man fell dead, a woman was found dead, the disciples saw someone who looked like a corpse.
By far the largest single use in the New Testament is the formula ek nekron, "from the dead" or "among the dead," which became the standard idiom for resurrection. Jesus is raised from the dead; he is the firstborn from the dead; believers are baptized into his death and raised as he was raised from the dead. This idiom is so fixed and so frequent that it shaped the creed, the letters, and Christian preaching from the beginning. Nearly half of all occurrences of the word fall into this pattern.
The word also functions as a substantive, "the dead," naming a class of people: those who have died and whose fate stands open to divine judgment or resurrection. "The living and the dead" became a paired formula for the whole of humanity, present and past.