How many letters does the top answer for “an influence that works subtly to lighten or modify something” have?

The most common answer is leaven (6 letters).

Crossword clue: an influence that works subtly to lighten or modify something

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

leaven 6 letters wn-def

an influence that works subtly to lighten or modify something

leavening 9 letters wn-def

an influence that works subtly to lighten or modify something