To bring into a state of unity; merge. To join (two or more substances) to make a single substance, such as a chemical compound; mix. To possess or exhibit in combination: The choreography, which combines artistry and athletics, is extremely innovative. To harvest (a grain crop) using a cutting, threshing, and cleaning machine. To become united; coalesce. To join forces for a common purpose. See Synonyms at join. Chemistry To form a compound. To harvest a grain crop using a cutting, threshing, and cleaning machine: "Norwegian bachelor farmers combining in their antique McCormacks\u201d ( Garrison Keillor). A power-operated harvesting machine that cuts, threshes, and cleans grain. An association of people or groups united for the furtherance of political or commercial interests. A combination.