A bomb was an explosive weapon.
Reegan gave Bruno Taltalian a bomb to kill the Third Doctor, but Reegan doublecrossed Taltalian and changed the timing on it. It exploded, killing Taltalian. However, the Doctor survived with minor injuries. (TV: The Ambassadors of Death)
The Z-Bomb was a doomsday weapon developed on Earth by 1986; with two or three placed at strategic positions around the globe, they had the potential to split the planet in half. (TV: The Tenth Planet)
After the Last Great Time War, the New Dalek Empire prepared a reality bomb aboard the Crucible, which they intended to use to destroy the entire multiverse save themselves. However, they were thwarted by the Children of Time, and the reality bomb was lost when the Crucible was destroyed. (TV: The Stolen Earth/Journey's End)
Daniel Barton left a bomb in his private aeroplane's cockpit as part of a trap left for the Thirteenth Doctor and her companions. The device was deadlocked to prevent them disarming it with a sonic screwdriver. (TV: Spyfall)
On Hedgewick's World of Wonders, the platoon stationed there possessed a bomb called the Desolator that could destroy a planet with orders to use it if Cybermen were encountered an unable to be defeated. Initially the Doctor was against using it, but after learning that there were three million Cybermen, he had Ludens Nimrod Kendrick Cord Longstaff XLI, the Emperor who was better known as Porridge activate it. The planet was destroyed along with all the Cybermen though one Cybermite survived. (TV: Nightmare in Silver)
During the 57th Segment of Time, a fission bomb was planted in the head of the giant Monoid statue aboard the Ark by Monoid One to destroy the enormous spacecraft and its human passengers. One of the super-strong Refusians moved the statue into the launching bay and it was ejected into space, where the bomb exploded harmlessly. (TV: The Ark)
In slang, "a bomb" was an expression which refered to a substantial amount of money. Isobel Watkins noted would make "a bomb" selling photographs to newspapers. (TV: The Invasion) In the 2000s, Gwen Cooper observed that old phones sold for "a bomb". (AUDIO: The Dead Line)