1. (n.) A sign made for the purpose of giving notice to a person of some occurrence, command, or danger; also, a sign, event, or watchword, which has been agreed upon as the occasion of concerted action.

2. (n.) A token; an indication; a foreshadowing; a sign.

3. (a.) Noticeable; distinguished from what is ordinary; eminent; remarkable; memorable; as, a signal exploit; a signal service; a signal act of benevolence.

4. (a.) of or pertaining to signals, or the use of signals in conveying information; as, a signal flag or officer.

5. (v. t.) To communicate by signals; as, to signal orders.

6. (v. t.) To notify by a signals; to make a signal or signals to; as, to signal a fleet to anchor.

ALGOL COBOL CRT spot DM display Doppler signal EDP FORTRAN IF signal IM display RF echoes Roman candle Teletype Wirephoto aid to navigation alarm alert alphabetic data alphanumeric code amber light angular data announce arresting assembler astonishing badge balefire banner beacon beacon fire beam beat signal beat the drum beckon bell bell buoy binary digit binary scale binary system bit blink blinker blips blue peter bounces broad hint broadcast bug buoy byte caution light celebrated channel character characteristic clue command pulses commands communicate communication communication explosion communication theory communicational communications compiler computer code computer language computer program consequential conspicuous control signals controlled quantity convey correcting signals cue data data retrieval data storage decoding device differentia dip dip the ensign display disseminate distinctive distinguished double-dot display dress ship earmark echo echo signal egregious electronic data processing eminent encoding entropy error error signals esteemed estimable exceptional exchange colors extraordinary fabulous facsimile famous fantastic feedback pulses feedback signals film data flag flag down flare flash fog bell fog signal fog whistle foghorn formidable gentle hint gesticulate gesture get across get over give give a signal give the nod give word glance glimmer glimmering go light goad gong buoy green light hail hail and speak half-mast hallmark hand on heliograph hexadecimal system high sign hint hoist a banner idiosyncrasy illustrious image impart impetus implication important incitement incredible index indicant indicate indication indicator individual information information explosion information theory inkling innuendo input data input quantity insignia insinuation instructions international alphabet flag international numeral pennant intimation keynote kick leave word leer local oscillator signal look machine language magnetotelephonic make a sign make a signal make known mark marked marker beacon marvelous measure memorable message microtelephonic momentous monotelephonic motion movement multiple messages noble nod noise notable note noteworthy noticeable notify nudge numeric data octal system of mark oscillograph data output data output quantity output signal outstanding parachute flare pass pass along pass on peculiar peculiarity phototelegraphic picture pilot flag pips play poke polar data police whistle prestigious prick prominent prompt property punch-card data quarantine flag radar signal radio radio beacon radiotelegraphic raise a cry random data rare reading rectangular data red flag red light redundancy reference quantity reflection remarkable rememberable render renowned report