How many letters does the top answer for “the act of joining; the thing joined or added.” have?

The most common answer is adjunction (10 letters).

Crossword clue: the act of joining; the thing joined or added.

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

adjunction 10 letters web-def

an act of joining or adjoining things

an act of joining or adjoining things 50% similar → adjunction