Definition of "kerplunk"

kerplunk

/kəˈplʌŋk/

noun
plural kerplunks
1. (informal) A sound of someone or something falling and landing heavily; a thud.
  Quotations
  If my life were a Saturday-morning cartoon, you would have heard a loud kerplunk as my stomach dropped. My poor starving stomach. It was under such stress already, and now this.
  2005, Michelle Tea, chapter 15, in Rose of No Man’s Land […], 1st Harvest edition, Orlando, Fla., Austin, Tex.: Harcourt, published 2007, page 125
2. (figuratively, US, slang, dated) A disappointment which comes as a surprise.
interjection
1. Used to indicate a thudding sound.
  Quotations
  We flipped to see who'd go first and I won, which meant Claudia had to dial. I called the number out loud for her, and inside me my heart was suddenly going "kerplunk, kerplunk, kerplunk," heavy as an elephant's feet.
  1986 November, Eva Bunting, chapter 7, in Sixth-grade Sleepover (An Apple Paperback), New York, N.Y.: Scholastic, page 41
verb
third-person singular simple present kerplunks, present participle kerplunking, simple past and past participle kerplunked
1. (intransitive, informal) To make the sound of falling and landing heavily; to thud.