'perilously-built' originates from the word 'perilous,' which comes from Old French 'perilleux,' derived from Latin 'periculosus,' meaning 'dangerous.' The suffix '-ly' is used to form adverbs, and 'built' is the past participle of 'build,' from Old English 'byldan.'

'perilous' changed from the Old French word 'perilleux' and eventually became the modern English word 'perilous.'

Initially, 'perilous' meant 'full of danger,' and this meaning has largely remained the same in modern usage.