1778, "carangoid fish of the West Indies and South Atlantic," highly esteemed for food, from American Spanish pampano, a name given to various types of fish, from Spanish, originally "vine, tendril," from Latin pampinus "tendril or leaf of a vine." In California, used of a different fish abundant in summer along the coast and also highly esteemed for food.
1550s, "disbelieve, give no credit to," from dis- "opposite of" + credit (v.). Meaning "show to be unworthy of belief" is from 1560s; that of "injure the reputation of, make less esteemed or honored" is from 1570s. As a noun, "want of credit or good repute," 1560s, from the verb. Related: Discredited; discrediting.