赤ちゃん|あかちゃんakachan[1]atamadaka (head-high)

1. nounbaby; infant
   その赤あかちゃんは歯はが生はえはじめている。↗

   The baby is cutting his teeth.

• Synonym赤ん坊あかんぼうNeutralA plainer word for a baby, with less of the affection of 「赤ちゃん」; can also mean someone naive about the world.
• Synonym赤子あかごWrittenWritten-style word for a baby; 「赤子の手をひねる」 uses it in a phrase for something very easy.
• Synonym乳児にゅうじWrittenWritten word for a baby under one year old, as in 「乳児健診」; the usual term in medical contexts.
• Synonym幼子おさなごWrittenWritten word for a young child; its range is wider than 「赤ちゃん」, taking in small children beyond babies.
• SynonymベビーNeutralLoanword for a baby, mostly used as a prefix, as in 「ベビーカー」.
• SynonymみどりごWrittenWritten, literary word for a newborn baby, with an archaic flavor; found mostly in literature.
• SynonymねんねCasualColloquial baby talk: means going to sleep or, affectionately, a baby; also a naive, childish young woman.
• Related幼児ようじNeutralNeutral word for a small young child (also written 「幼児」); stresses smallness and is not limited to babies.
• Related乳飲み子ちのみごWrittenWritten word for a baby still at the breast, as in 「乳飲み子を抱える」.
• Antonym老人ろうじんNeutralAntonym by age: an old person, the opposite end of life from 「赤ちゃん」.

「赤ちゃん」 is the default, affectionate word for a baby. For a plainer tone use 「赤ん坊」; in medical contexts 「乳児」; in written prose 「赤子」 or 「嬰児」; as a loanword prefix 「ベビー」. 「老人」 is the opposite in age.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 赤ん坊あかんぼうを親したしみをこめて言いった語ご。