'unsuspicious' originates from the prefix 'un-' meaning 'not' and the word 'suspicious', which comes from Latin 'suspiciōsus', where 'sus-' meant 'under' and 'specere' meant 'to look'.

'suspiciōsus' transformed into the Old French word 'suspicious', and eventually became the modern English word 'suspicious', with 'un-' added to form 'unsuspicious'.

Initially, 'suspicious' meant 'looking under or beneath', but over time it evolved into its current meaning of 'distrustful', with 'unsuspicious' meaning the opposite.