The threshold or the horizontal piece at the bottom of a doorway that you step over when entering or leaving.
From 'door' + 'sill' (from Old English 'syll' meaning a threshold or foundation, from Proto-Germanic roots). This compound directly describes the ground-level part of a door frame.
Doorsills in ancient Greek and Roman homes often had grooves worn into them from centuries of foot traffic—archaeologists can date occupancy and determine how many people lived in ancient homes by measuring doorsill wear patterns!
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