How many letters does the top answer for “cause to be interested or curious” have?

The most common answer is intrigue (8 letters).

Crossword clue: cause to be interested or curious

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

intrigue 8 letters wn-def

a crafty and involved plot to achieve your ends