• 牛乳ぎゅうにゅう — cow’s milk
• 母乳ぼにゅう — breast milk
• 乳児にゅうじ — infant
• 乳製品にゅうせいひん — dairy products
• 授乳じゅにゅう — breastfeeding
• 乳首ちくび — nipple

The character 乳 combines elements evoking a child and a hanging/dripping form — symbolizing milk and breastfeeding. It commonly appears in words about infants and dairy.

It’s indexed under the radical 乙 (“fishhook”) and functions as a つくり-type component in some compounds.

赤あかちゃんは 母乳ぼにゅうで 育そだてています。
The baby is being raised on breast milk.

乳製品にゅうせいひんを 控ひかえています。
I am avoiding dairy products.