Definition: The word "accustomed" in English has been used since the mid-19th century to refer to being accustomed to something, especially after having done it before. For example, "She's accustomed to being a mother by this age." In modern times, the term has become less specific and can also describe an animal being adapted to its environment through natural selection. It is often used when describing a habit that is habitual or automatic. The definition of the word "accustomed" can be as follows: 1) Being accustomed to something - When you are familiar with, or have done it before. 2) Describing an animal's adaptation to its environment - Through natural selection. For example, if an animal is naturally adapted to a particular food source but has not eaten it in a long time, it can be said that the animal "accustomed" to eating that food.