n.,obs. 1. An infamously losing text editor. Once, back in the 1960s, when a text editor was needed for the PDP-6, a hacker crufted together a quick-and-dirty 'stopgap editor' to be used until a better one was written. Unfortunately, the old one was never really discarded when new ones (in particular, TECO) came along. SOS is a descendant ('Son of Stopgap') of that editor, and many PDP-10 users gained the dubious pleasure of its acquaintance. Since then other programs similar in style to SOS have been written, notably the early font editor BILOS /bye'lohs/, the Brother-In-Law Of Stopgap (the alternate expansion 'Bastard Issue, Loins of Stopgap' has been proposed).
2. /sos/ n. To decrease; inverse of AOS, from the PDP-10 instruction set.