How many letters does the top answer for “the improbability of a specified outcome” have?

The most common answer is unlikelihood (12 letters).

Crossword clue: the improbability of a specified outcome

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

unlikelihood 12 letters wn-def

the improbability of a specified outcome

unlikeliness 12 letters wn-def

the improbability of a specified outcome

the probability of a specified outcome 50% similar → likelihood, likeliness