'long-billed' originates from English, as a compound of 'long' (from Old English 'lang', meaning 'long') and 'bill' (from Old English 'bile', meaning 'beak' or 'projection'), with the adjectival past-participle suffix '-ed'.

'long-billed' changed from earlier compound forms in Middle English (e.g. 'long-bill'd' or similar spellings) and eventually became the modern English 'long-billed'.

Initially it meant 'having a long bill' and over time this basic descriptive meaning has been retained in modern usage.