HSK 7-9
不由得
bùyóude动副
can't help; cannot but
听到孩子的回答她不由得点头。
Tīng dào hái zi de huí dá tā bù yóu de diǎn tóu.
She nodded involuntarily upon hearing the child's answer.
Say it
Hold the button, say it, then let go.
Other HSK words sharing a character
Also free:
Appears across levels (7-9) in the HSK 3.0 word list.