"Single letter" refers to a written or printed symbol that represents a sound or part of a word. It refers to individual letters of the alphabet, like A, B, or C, which can be used to create words and make up written language. Full definition
I was disappointed to only manage five teams with single letters, but it was a fruitful exercise, albeit much harder than I thought it would be when I began. (westhamway.net)
Children at four or five can learn the sounds for single letters and are able to read words like «hat,» «cat,» «sat,» and so on. (educationnext.org)
It lets you draw a line through the letters in a word rather tapping on single letters. (phoneradar.com)