One who domineers; a person who behaves arrogantly or tyrannically toward others.
From 'domineer' (Dutch/Latin origin + '-eer') + '-er' (agent noun suffix). This creates a somewhat redundant double-agent suffix (-eer already implies an agent), which is rare in English and suggests dialectal or non-standard usage.
The word 'domineerer' is almost never used because 'domineer' itself already contains an agent meaning—we'd normally just call such a person a 'domineerer' or more naturally a 'bully' or 'tyrant,' showing how English constantly prunes redundancy from its vocabulary.
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