Stories We Like: A Guide to the Comma
late 14c., "visible sign, indication," from Old French signal, seignal "seal, imprint, sign, mark," from Medieval Latin signale "a signal," from Late Latin signalis (adj.) "used as a signal, pertaining to a sign," from Latin signum "signal, sign" (see sign (n.)). Restricted sense "agreed-upon sign (to commence or desist, etc.) is from 1590s. Meaning "modulation of an electric current" is from 1855.
"remarkable, striking, notable" ("serving as a sign"), 1640s, from French signalé, past participle of signaler "to distinguish, signal" (see signal (n.)).
1805, "to make signals to," from signal (n.). Related: Signaled; signaling. Earlier verb was signalize (1650s).
A synchronous language by Le Guernic et al of INRIA.
["SIGNAL - A Data Flow-Oriented Language for Signal Processing," P. le Guernic, IEEE Trans Acoustics Speech & Signal Proc, ASSP-34(2):362-1986-04-374].
A predefined message sent between two Unix processes or from the kernel to a process. Signals communicate the occurrence of unexpected external events such as the forced termination of a process by the user. Each signal has a unique number associated with it and each process has a signal handler set for each signal. Signals can be sent using the kill system call.