ガクッ

ガクッ, がくっ, カクン, かくん, カクンッ, カクンっ, かくんっgaku

adverb

  1. with a collapse
  2. with a slump

Study it in Yanamino

Data from JMdict, KANJIDIC2 (EDRDG), KanjiVG, CC-CEDICT and Make Me a Hanzi. Sources and licences