How many letters does the top answer for “an enveloping or covering membrane or layer of body tissue” have?

The most common answer is adventitia (10 letters).

Crossword clue: an enveloping or covering membrane or layer of body tissue

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

adventitia 10 letters wn-def

an enveloping or covering membrane or layer of body tissue

tunica 6 letters wn-def

an enveloping or covering membrane or layer of body tissue