How many letters does the top answer for “one who, or that which, is joined.” have?

The most common answer is adjunctive (10 letters).

Crossword clue: one who, or that which, is joined.

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

adjunctive 10 letters web-def

joining; forming an adjunct

made or joined or united into one 50% similar → combined

not joined or united into one 50% similar → uncombined

one joined in a plot. dryden. 50% similar → complotter