How many letters does the top answer for “become thick or thicker” have?

The most common answer is inspissate (10 letters).

Crossword clue: become thick or thicker

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

inspissate 10 letters wn-def

become thick or thicker

thicken 7 letters wn-def

become thick or thicker

to become thick or thicker. 100% similar → incrassate