na-adjective
Describes objects that are physically thick and substantial, such as books, coats, or slices of meat. Often used attributively with な or as an adverb with に. The related i-adjective 分厚い is more common in everyday speech.
See also: 分厚い
この辞書は分厚で、持ち運びが大変だ。
This dictionary is thick and hard to carry around.
彼は分厚なコートを着て外に出た。
He put on a thick coat and went outside.
The i-adjective form is more common and colloquial than the adjectival noun 分厚. Both mean 'thick' or 'bulky', but 分厚い is used in a wider range of contexts.
A general word for 'thick'. 分厚 emphasizes greater thickness or bulkiness, often with a nuance of being impressively or inconveniently thick.
Compound of 分 (bu, 'part' or 'portion') and 厚 (atsu, 'thick'). The exact historical derivation is uncertain, but the combination intensifies the meaning of thickness.