'casually-assembled' originates from the English words 'casual' and 'assemble', where 'casual' meant 'relaxed or informal' and 'assemble' meant 'to gather or put together'.

'casual' and 'assemble' were combined in modern English to form the compound adjective 'casually-assembled'.

Initially, 'casual' meant 'relaxed or informal', and 'assemble' meant 'to gather or put together'. The combination retains these meanings in the context of being put together informally.