SOS
n. countablen. an urgent signal that someone needs help. You use it when you are in a dangerous situation and cannot get out alone.
n. an international distress signal used to request immediate assistance in an emergency. Originally used in Morse code, it is now a general term for any urgent call for help.
The lost hikers sent an SOS from the mountain top.
After the engine failed in the middle of the ocean, the captain immediately broadcast an SOS to nearby ships.
The flare was intended as a visual SOS, hoping to catch the attention of the rescue planes patrolling the coastline before nightfall.
From the letters represented by the signal, chosen as a sequence that is easy to recall and transmit (· · · — — — · · ·); it is not, as is commonly believed, an abbreviation for "save our souls", "save our ship", or any other phrase.
Often used as a modifier before another noun, such as 'SOS signal' or 'SOS call'.