'unreliable' originates from the prefix 'un-' meaning 'not' and the word 'reliable', which comes from the Latin 'reliabilis', meaning 'that may be relied on'.

'reliable' changed from the Latin word 'reliabilis' and eventually became the modern English word 'reliable'.

Initially, it meant 'that may be relied on', but over time it evolved into its current meaning of 'not able to be trusted or depended on'.