How many letters does the top answer for “by way of addition.” have?

The most common answer is additionally (12 letters).

Crossword clue: by way of addition.

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

additionally 12 letters web-def

in addition, by way of addition; furthermore

in addition, by way of addition; furthermore 67% similar → additionally

added; supplemental; in the way of an addition. 50% similar → additional