/ ˌpɪtəˈpæt; NAmE / (also ˈpitter-patter ) adverb
with quick light steps or beats :
Her heart went pit-a-pat.
► pit-a-pat (also pitter-patter ) noun [ sing. ]:
I could hear the pit-a-pat of feet in the corridor.
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WORD ORIGIN
early 16th cent.: imitative of alternating sounds.