Permission or the right to enter a place, or the physical property in electricity that measures how easily current flows.
From Old French 'admettre' (to admit), from Latin 'admittere' (to allow). The electrical meaning came from 'admit' in the technical sense.
The word 'admittance' in electronics is the opposite of 'impedance'—admittance measures how easy it is for electricity to flow, while impedance measures resistance, making them perfect opposite concepts.
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