verb

• (transitive) To make smaller.
  "The threat of terrorism to the British lies in the overreaction to it of British governments. Each one in turn clicks up the ratchet of surveillance, intrusion and security. Each one diminishes liberty."
• (intransitive) To become less or smaller.
  "Whether modern, industrial man is less or more warlike than his hunter-gatherer ancestors is impossible to determine.[…]One thing that is true, though, is that murder rates have fallen over the centuries, as policing has spread and the routine carrying of weapons has diminished. Modern society may not have done anything about war. But peace is a lot more peaceful."
• (transitive) To make appear smaller than in reality; to dismiss as unimportant.
  "Although British involvement in the slave trade prior to 1807 cannot be denied, or its effects diminished, it is also a fact that the Royal Navy was pretty much the only force in the world in the 19th century with the numbers, drive, willingness, firepower, and capability to curtail the global slave trade, and that, without these efforts, many more would no doubt have been taken to slave plantations and other such destinations during the 19th, and possibly even into the 20th, centuries, as it must be remembered that a great many European powers would only begrudgingly commit to ending the slave trade when the other option was continuous war with the British Empire."
• (transitive) To lessen the authority or dignity of; to put down; to degrade; to abase; to weaken; to nerf (in gaming).
  "It shall be the basest of the kingdoms; neither shall it exalt itself any more above the nations: for I will diminish them, that they shall no more rule over the nations."