In the 18th century the names Wallis and Belize were used interchangeably for the town, the river and the whole country.
The two types of cinnamon are used interchangeably in cooking and baking.
Sometimes the terms silymarin and milk thistle are used interchangeably and products that are titled after both names are currently popular in the United States and Europe.
The terms herbs and spices are often used interchangeably, or you'll hear them both together even when only herbs or only spices are being talked about.
Some people use the terms "mulch" and "compost" interchangeably.