sec·ond·ar·y / ˈsekənˌderē/ • adj. 1. coming after, less important than, or resulting from someone or something else that is primary: luck plays a role, but it's ultimately secondary to local knowledge. ∎  of or relating to education for children from the age of eleven to sixteen or eighteen: a secondary school. ∎  having a reversible chemical reaction and therefore able to store energy. ∎  relating to or denoting the output side of a device using electromagnetic induction, esp. in a transformer.2. (Secondary) Geol. former term for Mesozoic.3. Chem. (of an organic compound) having its functional group located on a carbon atom that is bonded to two other carbon atoms. ∎  (chiefly of amines) derived from ammonia by replacement of two hydrogen atoms by organic groups.• n. (pl. -ar·ies) 1. short for: ∎  a secondary color. ∎  Ornithol. a secondary feather. ∎  a secondary coil or winding in an electrical transformer.2. Football the players in the defensive backfield; the area these players cover.3. (the Secondary) dated Geol. the Secondary or Mesozoic era.DERIVATIVES: sec·ond·ar·i·ly / -ˌderəlē/ adv.sec·ond·ar·i·ness n.

secondary
1. One of the inner flight feathers of a bird, located on the trailing edge of the wing between the body and the bend of the wing.

2. Applied to structures (e.g. the limbs of snakes, the wings of insects) that have been lost in the course of evolution, and to structures or forms (e.g. bilateral symmetry in Nudibranchia) that have developed.