received letter; correspondence
Archaic term for a letter one has received; used in classical or formal written contexts. Modern Japanese would normally use 手紙 or 来信.
In old documents, you can find expressions like 'I have received your letter' using 来簡.
Archaic kanji spelling for a received letter; 簡 is an old term for letter or document.
Variant kanji spelling using 翰, also an old term for letter or writing brush.
Compound of 来 (rai, 'coming') and 簡 (kan, 'letter, document'). The exact historical derivation is uncertain, but it follows a classical pattern for received correspondence.