noun
love letter; billet-doux
A somewhat literary or old-fashioned term for a love letter. In modern casual speech, ラブレター is more common.
彼は彼女に艶書をしたためた。
He wrote a love letter to her.
この小説には美しい艶書のやりとりが描かれている。
This novel depicts an exchange of beautiful love letters.
Compound of 艶 (en, 'charming; romantic') and 書 (sho, 'writing; letter'). The reading えんしょ is the standard on'yomi; the alternative readings えんじょ and えんぞ are obsolete.