な形容詞（なけいようし、nakeiyoushi）
- na-adjective

The word な形容詞 （なけいようし), often translated as "na-adjective" or "adjectival noun," is one of the two main types of adjectives in the Japanese language. Unlike い形容詞 (i-adjectives), which end in い, な形容詞 are characterized by their use of な to connect them to nouns. They function similarly to nouns in their conjugation patterns, and modify nouns with a な.

⚫︎ きれいな花 Translation: Beautiful flower ⚫︎ 静かな図書館 Translation: Quiet library ⚫︎ 有名な歌手 Translation: Famous singer

⚫︎ な形容詞 are used to describe nouns. ⚫︎ When directly modifying a noun, な形容詞 is followed by な. For example: 元気な人（a healthy person). ⚫︎ When used as the predicate (the part of the sentence that makes a statement), な形容詞's conjugation resembles that of nouns. For example, the plain positive form is the word itself (e.g., 静か - quiet), the plain negative form is 静かじゃない (not quiet). The polite positive form is 静かです (is quiet) and the polite negative form is 静かじゃありません or 静かではありません (is not quiet). ⚫︎ They also take other particles like に and で to express different meanings. For example, 静かに勉強する (study quietly).

⚫︎ The word is typically written in hiragana as なけいようし. ⚫︎ It can also be written in katakana if used to represent a foreign word. ⚫︎ The kanji representation is not common, and learners typically encounter the word in hiragana.

There aren't direct synonyms for な形容詞 as it is a grammatical category. However, many individual な形容詞 have synonyms. For example: ⚫︎ きれい（beautiful) is similar to 美しい, though 美しい is an い形容詞. ⚫︎ 有名（famous) is similar to 著名な.

Similarly, there aren't direct antonyms for な形容詞 as a grammatical category. However, many individual な形容詞 have antonyms. For example: ⚫︎ 静か（quiet) contrasts with 賑やか（にぎやか）（lively). ⚫︎ 有名（famous) contrasts with 無名（むめい）（unknown).

このレストランは静かな形容詞 ・Translation: This restaurant is quiet. ・Explanation: This sentence uses the な形容詞 静か to describe the restaurant. Note the polite form is being used (です).

彼は親切な人です。 ・Translation: He is a kind person. ・Explanation: The な形容詞 親切, meaning "kind," is used to describe "person". The な connects the adjective to the noun.

The etymology of な形容詞 stems from their grammatical function. They are called な形容詞 because they connect to nouns using the particle な, which is a particle from the classical Japanese language. The term reflects their unique grammatical behavior in comparison to い形容詞.