'thick-beaked' is a Modern English compound formed from 'thick' + 'beaked', where 'thick' meant 'having great density or breadth' and 'beak' meant 'the bill of a bird'.

'thick' comes from Old English 'þicce' and developed into the modern adjective 'thick'; 'beak' comes via Middle English 'bek' from Old French 'bec' (from a Germanic source). These elements were compounded in Modern English to form 'thick-beaked'.

Initially it described literally 'having a thick beak' and has retained that primary, literal meaning in modern usage (often in ornithological descriptions).