2. Descriptive of being outdated or outmoded, as machinery or weapons.
3. In biology, gradually disappearing; imperfectly or only slightly evolving: An obsolescent development of an organ or other part of an animal or a plant.
2. The representation of someone or something as existing or happening in a completely different period of time than it should: The novel has one anachronism after the other.
It is an obsolete notion to wear a bustle which has become obsolescent for daily wear. It is somewhat of an anachronism, like wearing lace mitts to the opera because lace mitts are archaic, something my great grandmother wore; however, now they are just considered an archaism best left for the manikin in the museum.