noun
younger female cousin
Specifically a female cousin who is younger than the speaker. Compare 従姉 (older female cousin), 従弟 (younger male cousin), and 従兄 (older male cousin).
See also: 従姉
私の従妹は来年高校を卒業する。
My younger female cousin will graduate from high school next year.
夏休みに従妹が遊びに来た。
My younger female cousin came to visit during summer vacation.
The kanji 従 means 'follow' or 'obey', and 妹 means 'younger sister', together indicating a younger female relative. The reading いとこ is a jukujikun, a native Japanese word assigned to these kanji.