4. To work on something (typically a program). In an immediate sense: "What are you doing?" "I'm hacking TECO." In a general (time-extended) sense: "What do you do around here?" "I hack TECO." More generally, "I hack "foo"" is roughly equivalent to ""foo" is my major interest (or project)". "I hack solid-state physics." See Hacking X for Y.
7. Short for hacker.
8. See nethack.
9. (MIT) To explore the basements, roof ledges, and steam tunnels of a large, institutional building, to the dismay of Physical Plant workers and (since this is usually performed at educational institutions) the Campus Police. This activity has been found to be eerily similar to playing adventure games such as Dungeons and Dragons and Zork. See also vadding.