also: おんば
noun
A woman employed to breastfeed and care for another's child, historically common in aristocratic and samurai families. The term is now largely historical.
江戸時代、乳母は武家の子供の養育に重要な役割を果たした。
In the Edo period, wet nurses played an important role in raising children of samurai families.
彼女はその家の乳母として長年仕えた。
She served for many years as the family's wet nurse.
Alternate jukujikun reading; less common than うば.
The kanji 乳 (milk) and 母 (mother) directly convey the meaning. The reading うば is a jukujikun, a special reading assigned to the compound rather than derived from the individual kanji readings.