The early Chinese character for "客(kè)" was like a person getting into a house and temporarily living there.
请客(qǐngkè): treat sb.(to dinner etc.)
客厅(kètīng): living room
客气(kèqi): polite, courteous
Jīntiān wǒ qǐngkè.
It's my treat today.
Bú bì kèqi.
It was our pleasure.
Yào shuōfú kèhù yǐ zhège jiàgé gòumǎi，Duì wǒmen lái shuō hái zhēn bù róngyì.
We'll have a lot of difficulties in persuading our clients to buy at this price.