'unclog' originates from the prefix 'un-' meaning 'not' or 'opposite of' combined with 'clog', which comes from Middle English 'clogge', meaning 'block' or 'obstruction'.

'clogge' transformed into the modern English word 'clog', and with the addition of the prefix 'un-', it became 'unclog'.

Initially, 'clog' meant 'block' or 'obstruction', and 'unclog' evolved to mean 'remove the block or obstruction'.