'properly-built' originates from the combination of 'properly' and 'built', where 'properly' means 'in a suitable manner' and 'built' refers to the past participle of 'build', meaning 'to construct'.

'properly' changed from the Old French word 'propre' meaning 'own, individual', and 'built' from the Old English 'byldan', meaning 'to construct'.

Initially, 'properly-built' meant 'constructed in a suitable manner', and this meaning has largely remained the same in modern usage.