How many letters does the top answer for “identifying the nature or cause of some phenomenon” have?

The most common answer is diagnosing (10 letters).

Crossword clue: identifying the nature or cause of some phenomenon

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

diagnosing 10 letters wn-def

identifying the nature or cause of some phenomenon

diagnosis 9 letters wn-def

identifying the nature or cause of some phenomenon