How many letters does the top answer for “the greatest possible degree” have?

The most common answer is utmost (6 letters).

Crossword clue: the greatest possible degree

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

utmost 6 letters wn-def

the greatest possible degree

uttermost 9 letters wn-def

the greatest possible degree

the greatest possible degree of something 75% similar → limit