Origin: Latin suffix -ous
Simultaneous has 2 different meanings across 1 category:
occurring or operating at the same time
"a series of coincident events"
Happening at the same moment.
"The fireworks exploded simultaneously, lighting up the entire sky in a single flash."
In plain English: Simultaneous means happening at exactly the same time.
"The two alarms went off at exactly the same time, which was quite simultaneous."
The word comes from Medieval Latin simultaneus, which was derived from the Latin phrase simul meaning "together" or "at the same time." It originally described things occurring together in that shared moment.