Simultaneously means at exactly the same moment. Happen simultaneously, simultaneously translated, released simultaneously.
The exactness is the point: simultaneously claims the same instant, where at the same time can mean the same period. Simultaneous translation is done live as somebody speaks, which is a genuinely extraordinary skill. In relativity, whether two events are simultaneous depends on the observer, which is one of the strangest results in physics. Note simultaneous, simultaneity.
1adverbsimultaneouslyAt exactly the same moment.
“The two runners crossed the line simultaneously, so the race was a draw.”
simultaneously is a relation in time.
Proto-Indo-European
*sem-
Latin
simul — together, at the same time
Medieval Latin
simultaneus
English
simultaneous
English, today
simultaneously
Built from
From simultaneous + -ly. simultaneous comes from Medieval Latin simultaneus, from simultim (“at the same time, extended”), from Latin simul (“together, at the same time”); compare similar.
Etymology from Wiktionary, CC BY-SA