What are the best answers for “happening or existing or done at the same time”?

simultaneity, simultaneousness.

How many letters does the top answer for “happening or existing or done at the same time” have?

The most common answer is simultaneity (12 letters).

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

simultaneity 12 letters wn-def

happening or existing or done at the same time

simultaneousness 16 letters wn-def

happening or existing or done at the same time

existing at the same time 60% similar → coexistent, coexisting

happening at the same time 60% similar → coincidentally, coincidently

existing at the same time; contemporaneous. 50% similar → monochronic