Definition: Annexationist means someone who opposes or opposes a particular group or concept. It's the act of moving, usually voluntarily, another person or something else out from under or above them, often by taking away their property rights or rights to life, liberty, and property. The definition varies depending on context. Definition: An annexationist is someone who opposes or opposes a particular group or concept. They may take an action that challenges the status quo, often without being actively hostile to it, and oppose the idea of giving up one's own identity, values, rights, freedoms, or responsibilities under a different government, society, organization, etc. An example could be the United States annexing Canada as part of its territorial expansion.