A side road or secondary path that connects or branches off from a main route; a hanging-on or attached way.
Compound of 'hang' and 'by,' from Middle English usage where 'hang by' meant something connected but not primary. The word appears in older texts referring to auxiliary paths or secondary connections.
This is one of those wonderful old English words that shows how people described landscape features before we had standardized terms—a 'hangby' perfectly captured the idea of a road that seemed to just 'hang along' a main route without being quite as important.
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