A fishing float or bobber that bobs up and down on water to indicate when a fish bites.
From the verb 'dob' (to fish by letting the bait dip gently into the water), which comes from Middle English and possibly Low German origins. The '-er' suffix creates an agent noun for the thing that does the dobbing action.
The humble dobber is actually a perfect example of how fishing culture shaped English — before modern fishing reels, anglers used dobbing technique in shallow streams, and the bobber remains an iconic image in fishing even today.
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