A small building (or "vault") for the remains of the dead, with walls, a roof, and (if it is to be used for more than one corpse) a door. It may be partly or wholly in the ground (except for its entrance) in a cemetery, or it may be inside a church proper or in its crypt. Single tombs may be permanently sealed; those for families (or other groups) have doors for access whenever needed.
"The family gathered outside the stone tomb to place fresh flowers at their parents' gravesite before locking the heavy door for good."
In plain English: A tomb is an underground burial place where important people are kept after they die.
"The ancient king was buried in an elaborate stone tomb outside the city walls."
Usage: A tomb refers specifically to an enclosed structure like a vault or mausoleum designed to house human remains, distinguishing it from open graves or simple burial sites. These buildings often feature walls and roofs, sometimes with doors if intended for multiple occupants.
To bury.
"The ancient ritual required them to tomb the fallen king beneath a mound of earth."
From Middle English tombe, toumbe, borrowed from Old French tombe, from Latin tumba from Ancient Greek τύμβος (túmbos, "a sepulchral mound, tomb, grave"), probably from Proto-Indo-European *tewh₂- ("to swell"). The verb is from Middle English tomben.