1To tremble or shake (from fear, cold, or nervousness); chattering of teeth (onomatopoeic).
寒さで手がガクガク震えて字がうまく書けない。
My hands are trembling from the cold and I can't write well.
怖くて足がガクガクした。
I was so scared my legs were shaking.
緊張で声がガクガクしていた。
My voice was trembling from nervousness.
2To be loose or wobble; to come loose and shake (e.g., a shaky shelf or structure).
地震で棚がガクガク揺れて食器が落ちた。
The shelf wobbled in the earthquake and the dishes fell.
古い机の脚がガクガクしているので修理が必要だ。
The legs of the old desk are wobbly and need repair.
ネジが緩んでドアがガクガクする。
The screw is loose and the door wobbles.