'illicitly' originates from Latin, specifically the word 'illicitus,' where 'in-' meant 'not' and 'licitus' meant 'lawful.' 'Possessed' comes from Latin 'possessus,' the past participle of 'possidere,' meaning 'to have and hold.'

'Illicitus' transformed into the Old French word 'illicite,' and eventually became the modern English word 'illicit.' 'Possessus' evolved into the Old French 'possesser,' leading to the modern English 'possess.'

Initially, 'illicit' meant 'not allowed by law,' and this meaning has largely remained the same in modern usage. 'Possess' originally meant 'to have and hold,' which is consistent with its current meaning.