请柬
qǐng jiǎn · HSK 7
invitation card
💌 请柬 = 请 invite + 柬 note/letter = a written invite-note
请 qǐng is the same invite/please you know from 请客. 柬 jiǎn means a note or card. Put them together and you get the formal card that requests your presence.
请 — speech radical 讠 + 青 (qīng, blue/green)
请 is a semantic-phonetic compound. The speech radical 讠 (言) signals a meaning related to speaking, while 青 (qīng) supplies the sound. Originally it meant 'to ask' or 'request' through speech, and later extended to the polite 'please' and 'to invite'.