形容動詞（けいようどうし、keiyoudoうshi）
- na-adjective

The Japanese word 形容動詞 (けいようどうし, *keiyou doushi*) literally translates to "adjectival verb." They are a unique type of word in Japanese that functions like both an adjective and a verb. They describe the state or characteristics of a noun, similar to how adjectives do, but they also conjugate like verbs. This means they change form depending on tense and politeness. Essentially, 形容動詞 modify nouns in a descriptive way. They often express qualities, states, or conditions. They are also sometimes called "na-adjectives" because they always take the particle な (*na*) before the noun they modify.

Here are some examples of 形容動詞 in action: ⚫︎ 静かな図書館 Translation: a quiet library ⚫︎ きれいな花 Translation: a beautiful flower ⚫︎ 便利なアプリ Translation: a convenient app

形容動詞 are used to describe the characteristics or states of nouns. They always take the particle な (*na*) when directly modifying a noun. When used predicatively (at the end of a sentence), they conjugate like verbs, taking forms like です (*desu*) for politeness. Here's how they are typically used: ⚫︎ When modifying a noun directly: [形容動詞] + な + noun (e.g., 静かな部屋 *shizuka na heya* - a quiet room) ⚫︎ When used predicatively (at the end of a sentence): they take verb-like conjugations. (e.g., 部屋は静かです *heya wa shizuka desu* - The room is quiet.)

形容動詞 are usually written using a combination of kanji and hiragana, and sometimes katakana (for loanwords). The word 形容動詞 itself is written with the kanji 形容 and 動詞. The basic form of most 形容動詞 ends in hiragana, and conjugation involves changing the ending. The particle な (*na*) that follows the 形容動詞 when it modifies a noun is always written in hiragana. There are no variations in the okurigana for the 形容動詞 words. 形容動詞 words always end with "da" in its dictionary form. (e.g. 静かだ (shizuka da) 形容動詞 do not have a stem. There are a small number of 形容動詞 with irregular conjugations.

There aren't direct synonyms for 形容動詞 itself, as it's a grammatical term. However, words that can be expressed with a 形容動詞, and therefore carry a similar meaning, could be considered related. Some might include: ⚫︎ Adjectives (specifically, the adjectives that share the same function of describing nouns and taking the particle *na* to do so). ⚫︎ Descriptive verbs (while not synonyms in the strictest sense, some verbs can express similar ideas.)

Again, not direct antonyms for 形容動詞 itself, but words that express the opposite meaning or state described by a specific 形容動詞 could be considered antonyms. For example, the antonym of 静か (shizuka - quiet) could be 騒がしい (sawagashii - noisy) or 賑やか (nigiyaka - lively), or 活気がある (kakki ga aru - to be lively).

彼は親切な人です。 ・Translation: He is a kind person. ・Explanation: 親切 (shinsetsu - kind) is a 形容動詞. It is used with な before the noun 人 (hito - person) to describe the person, and it conjugates to です (desu) at the end of the sentence to show politeness.

このレストランは有名なレストランです。 ・Translation: This restaurant is a famous restaurant. ・Explanation: 有名 (yuumei - famous) is a 形容動詞. It is used with な before the noun レストラン (resutoran - restaurant) to describe the restaurant, and it conjugates to です (desu) at the end of the sentence to show politeness.

The etymology of 形容動詞 is straightforward. ⚫︎ 形容 (*keiyou*) means "adjective." ⚫︎ 動詞 (*doushi*) means "verb." Therefore, 形容動詞 is literally a compound word meaning "adjective verb," reflecting its dual nature as both descriptive and conjugatable.