How many letters does the top answer for “one who wrongfully or illegally seizes and holds the place of another” have?

The most common answer is supplanter (10 letters).

Crossword clue: one who wrongfully or illegally seizes and holds the place of another

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

supplanter 10 letters wn-def

one who wrongfully or illegally seizes and holds the place of another

usurper 7 letters wn-def

one who wrongfully or illegally seizes and holds the place of another