impedance

Etymology

It is formed from English impede + -ance,^{[2][3][4][5][6]} as a term introduced by Heaviside.^[7] Etymonline notes that the classically correct formation would be “impedience”.^[3] The verb comes from Latin impediō (“to shackle the feet; to hinder”),^[2][3] formed from in- and pēs (“foot”),^[2][3] from Proto-Indo-European *ped- (“foot”).^[3]

Earliest recorded meaning

The overall opposition of a circuit to an electric current, arising from its resistance and reactance: 1886, in Heaviside's Electrical Papers.^[2][3][4]

Semantic evolution

Etymonline defines the word as "hindrance", especially and originally the resistance in an electrical circuit due to induction.^[3] It was coined for alternating currents in 1886.^[2][3][7] From 1919 it was applied to analogous properties of vibrating mechanical systems in mechanics and acoustics, such as acoustic impedance and mechanical impedance.^[2][5][8] From 1935 it also named a component that has impedance and can be built into a circuit.^[2][8]

Timeline

• 1886 – the overall opposition of a circuit to an alternating current.^[2][3][4]
• 1919 – an analogous property of vibrating systems, in mechanics and acoustics.^[2]
• 1935 – a component that has impedance.^[2]

Meanings

Noun

1. The total opposition of a circuit to an alternating current, combining its resistance and reactance, measured in ohms.^[8][4][2]
2. A component of a circuit that has impedance.^[8][2]
3. In acoustics, the ratio of the sound pressure over a surface to the rate of flow through it (acoustic impedance).^[8][5][4]
4. In mechanics, the ratio of a force to the velocity of the vibration it produces (mechanical impedance).^[8][5]
5. Resistance to the passage of a substance, such as water vapour, through a film.^[4]

Word family

• acoustic impedance

Related words

• impediment
• impede
• expedite
• pedal

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
7. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
8. ^ a b c d e f Collins English Dictionary (2023), Glasgow: HarperCollins