'swiftly-gained' originates from the combination of 'swiftly' and 'gained', where 'swiftly' is derived from 'swift', meaning 'moving with great speed', and 'gained' is the past participle of 'gain', meaning 'to obtain or secure'.

'swiftly' changed from Old English 'swift' and 'gained' from Old French 'gaigner', eventually forming the modern English term 'swiftly-gained'.

Initially, 'swiftly' meant 'quickly' and 'gained' meant 'obtained', and this combined meaning has largely remained the same in modern usage.