HSK 7-9
磕
kē动
to tap; to knock (against sth hard); (esp.) to knock (mud from boots, ash from a pipe etc); (fandom slang) to be into (a character relationship, dynamic, or trope)
他下车时不慎磕到了膝盖。
Tā xià chē shí bú shèn kē dào le xī gài.
He accidentally knocked his knee while getting out of the vehicle.
Say it
Hold the button, say it, then let go.
Also free:
Appears across levels (7-9) in the HSK 3.0 word list.