妃 — queen, princess

そのイスラム教国王妃は第一子を出産した。

The Sultana gave birth to her first child.

例のダイアナ妃の本、さっそく買って読んだよ。

I bought the book about Princess Diana (everybody is talking about, you recommended, etc.) right away and read it.

当初東宮（のちの朱雀帝）妃にと希望されていたが、左大臣の思惑で元服した源氏の北の方に納まる（「桐壺」）。

She was, at first, intended to be the wife of the Crown Prince (Later Emperor Suzaku), but in accordance with the Sadaijin's plans, she became the lawful wife of Genji after he completed his initiation ceremonies into adulthood ('Kiritsubo' (The Paulownia Court)).