Meaning
The kanji 貝 means shell or shellfish. Its shape traces back to a pictograph of a cowrie shell: the two short strokes at the top represent the shell's halves opening slightly, and the lines below suggest the creature inside. Once you see the image, the character is hard to forget.
The character carries more weight than its appearance suggests. In ancient China, cowrie shells were used as currency — prized for their smooth surface and relative scarcity inland. That monetary history is preserved in modern kanji. Characters like 財 (wealth), 買 (to buy), 売 (to sell), 貨 (goods/cargo), and 費 (expense) all contain 貝, because shells were coins.
Written in 7 strokes, 貝 is a Grade 1 kyōiku kanji — Japanese children encounter it at age 6 or 7. For non-native learners, though, the vocabulary built around it places it firmly in the JLPT N2 range. 貝 also serves as its own radical (部首, bushu), appearing in dozens of common kanji.
Readings
On'yomi (音読み) — Chinese-derived readings
The on'yomi reading is バイ (BAI), drawn from the historical Chinese pronunciation. It appears mainly in academic, zoological, or archaeological compounds — rarely in ordinary speech.
- 貝 (bai) — shell, shellfish (formal/compound usage)
- 宝貝 (takarakai) — cowrie shell (the 貝 here is read かい in everyday use; バイ surfaces mainly in scientific nomenclature)
For practical conversation, バイ is a background reading. When you need to speak, reach for かい instead.
Kun'yomi (訓読み) — Native Japanese readings
The kun'yomi reading is かい (kai) — the one you will actually use. At a seafood restaurant, on the beach, or scanning a menu: it is always かい.
- 貝 (kai) — shell or shellfish, in general
- 貝殻 (kaigara) — an empty seashell
- 巻き貝 (makigai) — univalve; a spiral-shelled creature
- 二枚貝 (nimaigai) — bivalve (clam, oyster, scallop — literally "two-plate shell")
Common Words & Compounds
Vocabulary around 貝 spans seafood menus to archaeology:
Nature & Creatures:
- 貝 (kai) — shell, shellfish
- 貝殻 (kaigara) — empty seashell
- 巻き貝 (makigai) — univalve, spiral-shelled creature
- 二枚貝 (nimaigai) — bivalve (clam, mussel, oyster)
- 宝貝 (takarakai) — cowrie shell (literally "treasure shell")
Food & Cuisine:
- 貝柱 (kaibashira) — scallop adductor muscle; the round white piece used in sashimi and sushi
- 貝のバター焼き (kai no batayaki) — shellfish grilled with butter
- 貝のみそ汁 (kai no misoshiru) — miso soup with clams
History & Culture:
- 貝塚 (kaidzuka) — shell midden; ancient refuse heaps containing shells, among the most important archaeological sites in Japan
- 貝細工 (kaizaiku) — shellwork; crafts made from shells
- 貝合わせ (kaiawase) — a Heian-period matching game played with pairs of clam shells, considered the ancestor of modern card-matching games
Kanji Compounds Using 貝 as Radical:
- 財布 (saifu) — wallet (財 contains 貝)
- 買い物 (kaimono) — shopping (買 contains 貝)
- 貨物 (kamotsu) — cargo, freight (貨 contains 貝)
Example Sentences
海岸で貝殻を拾った。
Kaigan de kaigara wo hirotta.
I picked up seashells on the beach.
この貝は食べられますか？
Kono kai wa taberaremasu ka?
Can you eat this shellfish?
貝柱の刺身はとても甘い。
Kaibashira no sashimi wa totemo amai.
Scallop sashimi is very sweet.
子供たちは砂浜で貝を集めて遊んだ。
Kodomotachi wa sunahama de kai wo atsumete asonda.
The children played by collecting shells on the sandy beach.
縄文時代の貝塚が近くで発掘された。
Jōmon jidai no kaidzuka ga chikaku de hakkutsu sareta.
A Jomon-era shell midden was excavated nearby.
二枚貝は水をろ過して食べる生き物だ。
Nimaigai wa mizu wo roka shite taberu ikimono da.
Bivalves are creatures that feed by filtering water.
この地域では貝の養殖が盛んです。
Kono chīki dewa kai no yōshoku ga sakan desu.
Shellfish farming is thriving in this region.
平安時代の貴族たちは貝合わせを楽しんだ。
Heian jidai no kizoku-tachi wa kaiawase wo tanoshinda.
The aristocrats of the Heian period enjoyed the shell-matching game kaiawase.
昔、貝は貨幣として使われていた。
Mukashi, kai wa kahei to shite tsukawarete ita.
Long ago, shells were used as currency.
Memory Tip
Look at 貝 and imagine staring straight down at a clam on a table. The two short strokes at the top are the shell's halves opening, and the lines below are the creature inside — two little eyes peeking out of a shell.
Now connect shells to money. The kanji 買 (buy) and 財 (wealth) both hide 貝 inside them because shells were ancient coins. Whenever you spot 貝 inside another kanji, ask: does this involve money or trade? It usually does.