What is the meaning of pitter-patter?

noun

• A series of rapid tapping sounds.
  • usage: "she missed the pitter-patter of little feet around the house"

verb

• Rain gently.
  • usage: "It has only sprinkled, but the roads are slick"
  • synonyms: sprinkle, spit, spatter, patter
• Make light, rapid and repeated sounds.
  • usage: "gently pattering rain"
  • synonyms: patter

adverb

• As of footsteps.
  • usage: "he came running pit-a-pat down the hall"
  • synonyms: pit-a-pat, pitty-patty, pitty-pat
• Describing a rhythmic beating.
  • usage: "his heart went pit-a-pat"
  • synonyms: pit-a-pat, pitty-patty, pitty-pat