'green-light' originates from Modern English as a compound of 'green' and 'light', where 'green' is from Old English 'grēne' meaning 'green' and 'light' is from Old English 'lēoht' meaning 'light' or 'lamp'.

'green-light' was first used in the literal sense to mean the green signal of a traffic light (late 19th to early 20th century with the introduction of traffic signals) and later developed an idiomatic sense 'to give permission' (mid 20th century).

Initially, it meant 'the green signal on a traffic light' (literal), but over time it evolved into the figurative meaning of 'official permission to proceed'.