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"simultaneous" is also used as a crossword clue. If that's what you saw, the answer is often coincident (10 letters).
Definitions
occurring or operating at the same time
Word origin
From Medieval Latin simultaneus, from simultim (“at the same time, extended”), from Latin simul (“together, at the same time”); compare similar.
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer2 curated clues
01“Happening together”12 letters
02“All at once”12 letters
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