Where does “billentyű” come from?

billentyű (Hungarian) comes from Hungarian billen, from Hungarian billeg — to sway, waggle.

billentyű (Hungarian): key; valve

Definitions

Step	Language	Word	Meaning
1	Hungarian	billen	to tilt, slant, lean, swing, dip
2	Hungarian	billeg	to sway, waggle

billentyű — Etymology, Origin & Word History | Etymology Explorer