The practice of working or travelling together with at least one other person, especially when undertaking something potentially risky or hazardous.

An organ system that coordinates the activities of muscles, monitors organs, constructs and processes data received from the senses, and initiates actions.

(anatomy, immunology) The system that differentiates self from non-self and protects the body from foreign substances and pathogenic organisms by producing an immune response. It includes organs such as the thymus, the spleen and lymph nodes; tissue such as bone marrow, and lymphoid tissues such as the tonsils; cells such as lymphocytes including the B cells and T cells, and cell products such as antibodies.

(astronomy) The combined system or structure formed by all of the rings orbiting a planet

(anatomy) A system of organs for the purpose of digesting food.

(taxonomy) A coherent system of taxonomic judgements on circumscription and placement of the considered taxa. A taxonomic system is restricted to a large but limited part of the living world.

A system used to determine the result of an election based on the preferences expressed by voters.

(anatomy) The skin, feathers and other outer coverings of an animal.

feudalism

A burglar alarm.