乳児(にゅうじ)

にゅうじ
noun
infant, baby
formalfamilyhealth
1. infant, baby
A baby, especially one still being breastfed or bottle-fed, typically from birth to about one year old. This is the formal/medical term.
乳児(にゅうじ)を抱(だ)いた母親(ははおや)がいた。
There was a mother holding an infant.
この薬(くすり)は乳児(にゅうじ)には使(つか)えません。
This medicine cannot be used on infants.
乳児(にゅうじ)健診(けんしん)で赤(あか)ちゃんの成長(せいちょう)を確認(かくにん)してもらった。
We had the baby's growth checked at the infant health checkup.

Usage: 乳児(にゅうじ) is the formal and medical term for an infant. In casual conversation, 赤(あか)ちゃん is far more common. The character 乳(にゅう) means "milk" or "breast," reflecting that the infant is at the nursing age.

Common collocations

  • 乳児(にゅうじ)健診(けんしん) (infant health checkup)
  • 乳児(にゅうじ)院(いん) (infant home, nursery institution)
  • 乳児(にゅうじ)用(よう) (for infants)

Age terminology

Related Words

Related: 幼児(ようじ) (toddler)
Related: 児童(じどう) (child (school-age))
Synonym: 赤(あか)ちゃん (baby (casual))
Compare: 赤ん坊 (baby)
Compare: 小児(しょうに) (child)
general
Added 2026.2.16 16:35 · Revised 2026.9.2 13:01
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