How many letters does the top answer for “placed on or over something else” have?

The most common answer is overlying (9 letters).

Crossword clue: placed on or over something else

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

overlying 9 letters wn-def

placed on or over something else

something placed at the center of something else (as on a table) 60% similar → centerpiece, centrepiece

standing for something else 50% similar → representative

to annex with something else. 50% similar → coannex