In every place or location; everywhere.
From Old English 'æ̅c' (each) + 'hwær' (where), combining each with where to create a comprehensive location marker. The word fell out of common use as 'everywhere' became standardized in Middle English.
This is a ghost word from Old English—you can see how modern English consolidated multiple ways of saying the same thing, keeping 'everywhere' while 'eachwhere' vanished from living speech by the 1500s, even though it perfectly follows English word-building logic.
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