How many letters does the top answer for “in a serious manner” have?

The most common answer is earnestly (9 letters).

Crossword clue: in a serious manner

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

earnestly 9 letters wn-def

in a serious manner

seriously 9 letters wn-def

in a serious manner

a manner that is serious and solemn 67% similar → graveness, soberness, somberness