MOB - An unruly group of people.
MOO - The characteristic sound made by a cow or bull.
TOO - Likewise.
BOO - A loud exclamation intended to scare someone, especially a child. Usually used when one has been hidden from the victim and then suddenly appeared unexpectedly.
BOT - The larva of a bot fly, which infests the skin of various mammals, producing warbles, or the nasal passage of sheep, or the stomach of horses.
TOT - A small child.
BOOM - To make a loud, resonant sound.
BOOT - A heavy shoe that covers part of the leg.
TOMB - 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.
MOOT - Subject to discussion (originally at a moot); arguable, debatable, unsolved or impossible to solve.
TOOT - The noise of a horn or whistle.
MOTTO - A sentence, phrase, or word, forming part of an heraldic achievement.
BOTTOM - The lowest part from the uppermost part.