'unseaworthy' originates from the prefix 'un-' meaning 'not' and the word 'seaworthy', which comes from 'sea' and 'worthy', where 'worthy' meant 'fit or suitable'.

'unseaworthy' evolved from the combination of 'un-' and 'seaworthy', which was used in Middle English as 'seawerþi', eventually becoming the modern English word 'unseaworthy'.

Initially, it meant 'not fit for sea travel', and this meaning has largely remained the same in modern usage.