燃 is a literary verb meaning 'to burn' or 'to ignite', often appearing as a stand-alone word in formal or written contexts. It is the core morpheme in common compounds like 燃烧 (to burn), 燃料 (fuel), and 燃放 (to set off fireworks). In everyday speech, 烧 or 点 are more frequent; 燃 carries a slightly more elevated or technical tone.