A person who speaks rapidly and unintelligibly; someone who produces gibblegabble.
From 'gibblegabble' plus the English agent suffix '-er,' creating a noun for a person who performs the action of gibblegabbling.
The suffix '-er' in English is incredibly productive—we automatically understand 'gibblegabbler' means 'one who gibblegabbles' even if we've never heard the word before, which shows how predictable English word-building actually is!
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