bastion

noun
  1. 1

    A projecting part of a rampart or other fortification.

  2. 2

    A well-fortified position; a stronghold or citadel.

  3. 3

    A person, group, or thing, that strongly defends some principle.

verb
  1. 1

    To furnish with a bastion.

Source: https://en.wiktionary.org/wiki/bastion