'open-billed' originates from English, a compound of the adjective 'open' and the noun 'bill' with the adjectival suffix '-ed', literally meaning 'having a bill that is open'.

'open' comes from Old English 'open' (meaning 'not closed'), and 'bill' (meaning 'beak' or 'projecting edge') comes from Old English 'bil'/'bile'; the compound form 'open-billed' developed in Modern English as a descriptive adjective for birds and objects with an open bill.

Initially it meant simply 'having an open bill' in a literal sense; over time it remained literal but also became a stable descriptive term used particularly in ornithology to identify species with a distinctive gap in the bill.