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)
Brian Williams suggested, among other theories, that the millions of Shakri cubes that suddenly appeared on Earth were bombs. (TV: The Power of Three)
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)