'narrow-billed' originates from English, specifically the words 'narrow' and 'bill', where 'narrow' originally meant 'small in width' and 'bill' meant 'beak'.

'narrow' changed from Old English 'nearwe' (later Middle English 'narwe') and became Modern English 'narrow'; 'bill' appeared in Middle English as 'bile'/'bille' meaning 'beak' and developed into Modern English 'bill'; the compound 'narrow-billed' arose in Modern English by combining these elements.

Initially, 'narrow' meant 'small in width' and 'bill' meant 'beak'; over time the compound came to be used specifically to describe birds with relatively thin beaks and has retained that descriptive meaning.