: a tool usually of hardened steel with cutting ridges for forming or smoothing surfaces (as of a tooth)
: a narrow instrument for shaping fingernails with a fine rough metal or emery surface
—filetransitive verb, filedfil·ing
In hardware and metalworking, bar- or rod-shaped tool of hardened steel with many small cutting edges raised on its surfaces. Files are used for smoothing or forming objects, especially of metal. A file's cutting or abrading action results from rubbing it, usually by hand, against the workpiece. The single-cut file has rows of parallel teeth cut diagonally across the working surfaces. The double-cut file has rows of teeth crossing each other. Rasp teeth are disconnected and round on top; rasp files are usually very coarse and are used primarily on wood and soft materials.