How many letters does the top answer for “the light horny waterproof structure forming the external covering of birds” have?

The most common answer is feather (7 letters).

Crossword clue: the light horny waterproof structure forming the external covering of birds

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

feather 7 letters wn-def

the light horny waterproof structure forming the external covering of birds

plumage 7 letters wn-def

the light horny waterproof structure forming the external covering of birds

plume 5 letters wn-def

the light horny waterproof structure forming the external covering of birds