1. n. A program used primarily to create, manipulate, modify, or analyze other programs, such as a compiler or an editor or a cross-referencing program. Oppose app, operating system. 2. [UNIX] An application program with a simple, `transparent' (typically text-stream) interface designed specifically to be used in programmed combination with other tools (see filter). 3. [MIT general to students there] vi. To work; to study (connotes tedium). The TMRC Dictionary defined this as "to set one's brain to the grindstone". See hack. 4. [MIT] n. A student who studies too much and hacks too little. (MIT's student humor magazine rejoices in the name `Tool and Die'.)