How many letters does the top answer for “another word for assertion” have?

The most common answer is asseveration (12 letters).

Crossword clue: another word for assertion

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

asseveration 12 letters gen-syn

a declaration that is made emphatically (as if no supporting evidence were necessary)

averment 8 letters gen-syn

a declaration that is made emphatically (as if no supporting evidence were necessary)

another word for about 50% similar → approximately, roughly, some

another word for terms 50% similar → footing

another word for under 50% similar → nether

another word for word 50% similar → phrase