How many letters does the top answer for “in a vigorous and effective manner” have?

The most common answer is trenchantly (11 letters).

Crossword clue: in a vigorous and effective manner

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

trenchantly 11 letters wn-def

in a vigorous and effective manner

in an effective manner 67% similar → effectively, efficaciously

in a lusty or vigorous manner. 50% similar → lustily

with vigor; in a vigorous manner 50% similar → vigorously