がくんと

adverb

suddenly; with a jerk

Describes a sudden, sharp movement or change, often implying a jolt or abrupt drop. Common with verbs like 落ちる, 下がる, 止まる.

• エレベーターががくんと止とまった。

  The elevator stopped with a jerk.

• 気き温おんががくんと下さがった。

  The temperature dropped suddenly.