'avast' originates from Dutch or Low German, specifically from the phrase 'hou vast' (or Middle Dutch 'houvast'), where 'hou' meant 'hold' and 'vast' meant 'fast' or 'firmly'.

'avast' changed from the Dutch phrase 'hou vast' (literally 'hold fast') into an interjection used by sailors in English; it entered nautical English from contact with Dutch and Low German seafarers in the 16th–17th centuries and became the short exclamation 'avast'.

Initially it meant 'hold fast' (a literal instruction to grip or secure something), but over time it evolved into a general command meaning 'stop' or 'cease' in maritime and colloquial usage.