nipple mouse = N = no-op

NMI /N-M-I/ n.

Non-Maskable Interrupt. An IRQ 7 on the PDP-11 or 680[01234]0; the NMI line on an 80123486. In contrast with a priority interrupt (which might be ignored, although that is unlikely), an NMI is never ignored. Except, that is, on clone boxes, where NMI is often ignored on the motherboard because flaky hardware can generate many spurious ones.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.