A person who talks excessively or reveals secrets thoughtlessly.
From 'blabber' (to talk excessively) plus '-er' (one who does the action). The root likely comes from imitative sound patterns.
Most languages have a unique insult for someone who talks too much—English has 'blabberer,' but other languages like Dutch have 'klapkous' (chatter jaw). It shows how universal the annoyance of excessive talking is!
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