What does 怪獣 Kaiju mean?
Kaiju (怪獣) means strange beast, or simply monster. The giant part is carried by the dai- prefix in daikaiju, not by the word itself.
- Written
- 怪獣 (kaijū)
- Literally
- 怪 (kai, strange or suspicious) with 獣 (juu, beast). A strange beast, normally translated monster. Nothing in it means large.
- As slang
- Ordinary vocabulary. A child describing a monster in a picture book is using the same word as a film critic writing about Godzilla.
- In anime
- English treats it as a genre meaning city-levelling giants. The size lives in a separate prefix, and the word alone just means monster.
Kaiju means monster. The characters give strange beast, and there is nothing in the word about size, cities, or the sea.
The characters, one of them familiar
怪 (kai) is the strange, the suspicious, the not-right. It is the same character that opens yokai, which is a useful coincidence: the two words are cousins, both organised around the idea of something being off rather than around what the thing is.
獣 (juu) is a beast, an animal in the wild-and-four-legged sense. The compound arrived from Chinese with both characters carrying roughly these meanings.
Where the giant went
Into a prefix. 大 (dai) means great or large, and 大怪獣 (daikaijū) is the form reserved for the enormous ones, translated as giant monster on posters for exactly that reason.
Which means the English usage has absorbed a modifier that Japanese states separately. English speakers saying kaiju almost always mean daikaijū, and the plain word covers monsters of any dimension, including quite small ones.
The genre reading
English has made it a genre label: kaiju film, kaiju series, kaiju as a category on a streaming menu. Japanese can use it that way in compounds, but the bare word does not carry a genre any more than monster does in English.
This is the same move that happened to mecha, and it happened for the same reason. English needed a name for a body of work and reached for the most distinctive-sounding Japanese noun in the vicinity, which is how a word meaning monster came to imply a specific film tradition, a scale, and a set of expectations about property damage.
Why English wanted the loan at all
Because monster movie is accurate and useless. It covers a haunted house, a creature in a lake and a city being flattened, and the last of those is a distinct tradition with its own conventions, effects history and tone.
English had no term for it, borrowed one, and got a word that is broader in its own language than in the borrowing. That is the fourth entry on this site to end in that sentence, which is starting to look less like a coincidence and more like how borrowing works.
Quick answers
What does kaiju mean?
怪 (kai, strange or suspicious) with 獣 (juu, beast). A strange beast, normally translated monster. Nothing in it means large.
Is kaiju an insult?
Ordinary vocabulary. A child describing a monster in a picture book is using the same word as a film critic writing about Godzilla.
What does kaiju mean in anime?
English treats it as a genre meaning city-levelling giants. The size lives in a separate prefix, and the word alone just means monster.