1. vt. To cause to be broken (in any sense). “Your latest patch to the editor broke the paragraph commands.”
2. v. (of a program) To stop temporarily, so that it may debugged. The place where it stops is a breakpoint.
3. [techspeak] vi. To send an RS-232 break (two character widths of line high) over a serial comm line.
4. [Unix] vi. To strike whatever key currently causes the tty driver to send SIGINT to the current process. Normally, break (sense 3), delete or control-C does this.
5. break break may be said to interrupt a conversation (this is an example of verb doubling). This usage comes from radio communications, which in turn probably came from landline telegraph/teleprinter usage, as badly abused in the Citizen's Band craze of the early 1980s.