'liquid-filled' is a compound of 'liquid' + 'filled'. 'liquid' originates from Latin, specifically the word 'liquidus', where 'liquidus' meant 'fluid, flowing'; 'filled' comes from Old English, specifically the verb 'fyllan', meaning 'to fill'.

'liquid' came into English via Latin 'liquidus' and Old French forms into Middle English as 'liquid'; 'fill' developed from Old English 'fyllan' to Middle English 'fillen' and modern English 'fill' (past participle 'filled'). The compound 'liquid-filled' is a modern English adjectival compound formed by joining these elements.

Initially, 'liquid' referred to the quality of being fluid and 'fill' meant 'to make full'; combined as 'liquid-filled' the meaning is straightforwardly 'made full of liquid', which has remained stable in modern usage.