How many letters does the top answer for “having an exceptionally large head and brain” have?

The most common answer is macrocephalic (13 letters).

Crossword clue: having an exceptionally large head and brain

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

macrocephalic 13 letters wn-def

having an exceptionally large head and brain

macrocephalous 14 letters wn-def

having an exceptionally large head and brain

having a large brain. 60% similar → macrencephalic, macrencephalous