プログレッシブ和英中辞典(第4版)の解説
がくっ（と）
❶〔倒れる様子〕
ゴールに飛び込んだとたんに走者はがくっと膝を折って倒れた
Just as the runner crossed the finish line, his knees buckled and he collapsed.
❷〔変わる様子〕
今月は収入ががくっと減った
My income really plunged [plummeted/《口》 took a nose dive] this month.
❸〔衝撃を受ける様子〕
落選してがくっときている
I feel like the bottom has fallen out of my world since I lost the election.