貝・介|かいkai[1]atamadaka (head-high)

1. nounshellfish
   私が手てにしてるのは貝かいの化石かせきです。↗

   What I have in my hand is a fossil seashell.
2. nounseashell; shell

• SynonymシェルNeutralLoanword for a shell or outer casing, mostly in names and computer terms; everyday talk of seashells uses 「貝殻」 or 「貝」.
• Synonym殻からNeutralCovers all kinds of outer shells and husks, as in 「卵の殻」, and also shed empty shells; broader in range than 「貝」 and never means the shellfish itself.
• Synonym貝殻かいがらNeutralRefers specifically to a shellfish's shell, as in 「貝殻を拾う」; 「貝」 itself covers both the living shellfish and its shell.
• Related殻からNeutralCovers all kinds of outer shells and husks, as in 「卵の殻」, and also shed empty shells; broader in range than 「貝」 and never means the shellfish itself.
• Related甲羅こうらNeutralThe hard shell of turtles, crabs and the like; by extension also a person's back or years of experience. Not used for clams, snails or other molluscs.
• Related甲こうWrittenWritten/formal word for a carapace or shell, also first in rank and the instep or back of the hand; rarely stands alone — everyday speech says 「甲羅」.
• Related甲殻こうかくWrittenWritten/formal term for the carapace of crustaceans such as shrimp and crabs, as in 「甲殻類」; leans biological and is not used for the shells of clams or snails.

「貝」 covers both the shellfish and its shell. For the shell alone say 「貝殻」; for shells and husks in general 「殻」; for turtle and crab shells 「甲羅」; for crustacean shells in formal, biological use 「甲殻」. 「シェル」 is a loanword for casings and computer terms.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. （かい）軟体動物なんたいどうぶつのうち、一般いっぱんに硬かたい殻からを持もつもの。