'ecologically-sound' originates from the combination of 'ecology' and 'sound', where 'ecology' refers to the study of organisms and their environment, and 'sound' means 'in good condition'.

'Ecologically-sound' evolved from the increasing awareness of environmental issues in the late 20th century, combining 'ecology' with 'sound' to emphasize sustainability.

Initially, it meant 'in good environmental condition', but over time it evolved into its current meaning of 'environmentally friendly or sustainable'.