(Biology) nervous system, the mechanism concerned with the correlation and integration of various bodily processes and the reactions and adjustments of the organism to its environment

central nervous system

tribal system

immune system

the limbic system, the part of the brain involved in our behavioural and emotional responses

economic system

decimal system

outmoded set-up, system or order

habit, way of life, disposition, custom, practice, conduct

polyandry

(Biology) the natural management of cells

Reproductive system.

system of education or instruction

feudalism, feudal system

solar system