'gill-breathing' originates from the combination of 'gill,' referring to the respiratory organ of aquatic animals, and 'breathing,' meaning the process of inhaling and exhaling air.

'gill' comes from Old Norse 'gil,' meaning 'ravine,' but in this context, it refers to the respiratory organ. 'Breathing' comes from Old English 'brēaþ,' meaning 'breath.'

Initially, it referred to the act of breathing through gills, and this meaning has remained consistent over time.