noun
breast pump
Specifically a device for expressing breast milk; commonly used in parenting and medical contexts.
See also: 搾乳
産院でさく乳器の使い方を教わった。
I learned how to use a breast pump at the maternity hospital.
酪農家は新しい搾乳器を導入した。
The dairy farmer introduced a new milking machine.
搾乳 is the act of milking or expressing milk, while 搾乳器 is the device used for that purpose.
Compound of 搾乳 (milking) + 器 (device). The exact historical origin is uncertain, but the kanji composition transparently reflects the meaning.