noun, noun or participle which takes 'suru', intransitive verb
A physical opening or aperture, often in technical contexts such as pipes, structures, lenses, or cameras. As 開口する, it can describe an opening being open or gaping in a technical way.
作業後、配管の開口をふさいだ。
After the work, we covered the opening in the pipe.
レンズの
The larger the lens aperture, the more light it can take in.
noun, noun or participle which takes 'suru', intransitive verb
opening one's mouth
Formal or technical wording for opening the mouth, especially in medical, dental, or examination contexts; everyday speech more often says 口を開ける.
歯科医に「大きく開口してください」と言われた。
The dentist told me, "Please open your mouth wide."
noun, noun or participle which takes 'suru', intransitive verb
beginning to speak; opening one's mouth to speak
A written or somewhat formal use meaning to start speaking after silence. It is also familiar in the set expression 開口一番, meaning 'the first thing someone says.'
彼はしばらく黙ったあと、ようやく開口した。
After staying silent for a while, he finally began to speak.
彼女は開口一番、「本当にすみません」と謝った。
The first thing she said was, "I'm truly sorry."
noun-modifying (irregular)
Limited prenominal or compound-form use meaning open or wide-open, as in terms such as 開口状態 or 開口母音. It is not normally used as a free adjective like English 'open.'
検査中は開口状態を保ってください。
Please keep your mouth open during the examination.
音声学では、開口母音は口の開きが大きい母音を指す。
In phonetics, an open vowel refers to a vowel pronounced with a wide mouth opening.