noun
very young bride; child bride; childish wife
Refers to a wife who is very young, often implying she is still childlike or was married at a young age. Can carry a slightly negative or pitying tone.
彼は幼妻をもらった。
He took a very young bride.
その村では幼妻がまだ見られる。
Child brides can still be seen in that village.
若妻 means 'young wife' in a more neutral or positive sense, without the implication of being childlike or too young.
Compound of 幼 (osana, 'very young, childish') + 妻 (tsuma, 'wife'), with rendaku voicing tsuma → zuma.