How many letters does the top answer for “the principal or ruling evil spirit. e. arnold.” have?

The most common answer is mara (4 letters).

Crossword clue: the principal or ruling evil spirit. e. arnold.

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

mara 4 letters web-def

hare-like rodent of the pampas of Argentina