The following is about the brewing term; adjunct is also a term used in linguistics.

In beer making and homebrewing, an adjunct is an ingredient other than water, barley, hops, and yeast. Typically, adjuncts are used by beer companies to reduce production costs and meet a taste profile exemplified by most North American lagers. Corn and rice are common adjuncts; Anheuser-Busch is the largest North American buyer of U.S. rice.

Less typically, fruit, spices, honey, and wheat are used as flavoring adjuncts.