空洞（くうどう、kuudoう）
- hollow/cavity

The Japanese word 空洞空洞 (くうどう) primarily means "hollow," "cavity," or "void." It refers to a space that is empty or lacking contents within a solid object or structure. It can describe physical spaces, metaphorical emptiness, or lack of substance. The 空洞 can be a physical space like a cave or a hole, or it can be used to describe an abstract concept like the 空洞 of a heart or the 空洞 of an argument.

⚫︎木の幹に空洞がある。 Translation: There is a cavity in the tree trunk. ⚫︎彼の話は内容が空洞だ。 Translation: His story is empty of content. ⚫︎歯に空洞ができた。 Translation: A cavity formed in my tooth.

This word is useful in various contexts. * When discussing physical spaces that are empty inside. * When describing something lacking substance or meaning. * In the medical context (e.g., cavities in teeth, or voids in the body). * In architecture and construction. * When describing the absence of something important, like emotional depth or intellectual substance.

* The word is primarily written using the kanji 空洞空洞. * The reading is くうどう (kūdo) in hiragana. * There are no variations in okurigana for this word.

* 穴 (ana) - hole, pit * 空間 (kūkan) - space * 虚無 (kyomu) - void, emptiness * 内部 (naibu) - interior, inside (can imply an empty inside) * 中空 (chūkuu) - hollow, cavity (can refer to something hollow inside).

* 充実 (jūjitsu) - fulfillment, being full, substantial * 中身 (nakami) - contents, what's inside * 固体 (kotai) - solid * 実質 (jisshitsu) - substance, essence

古い洞窟には大きな空洞が広がっていた。 ・Translation: A large cavity spread out in the old cave. ・Explanation: This sentence describes a physical space (the cave) that has a large, empty area inside.

彼の説明は空洞で、具体性に欠けていた。 ・Translation: His explanation was hollow and lacked specificity. ・Explanation: This sentence uses 空洞 metaphorically to indicate that the explanation was lacking substance and detail.

空 (kū) means "empty" or "sky," and 洞 (dō) means "cave," "hole," or "cavity." The combination of these kanji creates the meaning of an empty space or cavity.