What word starting with N is the opposite of thin?

The word "thin" has numerous opposites: wide, thick, broad, fat, stout, hefty, and substantial; and the verbs thicken, widen, broaden, repopulate, replenish, compress, or concentrate.

Conspicuously absent are antonyms that begin with the letter N. The closest might be natural for unthinned growth. Or the trivial "not thin."

It is possible that this is asking for the synonym, not the antonym.

(A close synonym is narrow.)