How many letters does the top answer for “of or concerning this” have?

The most common answer is hereof (6 letters).

Crossword clue: of or concerning this

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

hereof 6 letters wn-def

of or concerning this

of or concerning this or that 100% similar → thereof

of or concerning terminology 50% similar → terminological

of, or concerning thunder. 50% similar → fulmineous