1
Stage 1 of 3
al-'idada
Arabic · medieval
"the pointer, rule"
literally "the revolving radius" or pointer of a measuring circle
2
Stage 2 of 3
alhidada
Medieval Latin · 1400s
"sighting rule"
adopted through translated Arabic astronomical and surveying texts
3
Stage 3 of 3
alidade
English · 1400s
"sighting device for angle measurement"
entered English as the name for the sighting arm of a surveying instrument
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