How many letters does the top answer for “having a relatively long head with a cephalic index of under 75” have?

The most common answer is dolichocephalic (15 letters).

Crossword clue: having a relatively long head with a cephalic index of under 75

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

dolichocephalic 15 letters wn-def

an adult with a long narrow head