Full of hazards; dangerous, risky, or containing many dangers and risks.
From 'hazard' plus the suffix '-ful' meaning 'full of' or 'characterized by,' directly describing something laden with danger.
Words ending in '-ful' are oldest in English—'hazardful' sounds less natural than 'hazardous' because '-ous' is more common now, showing how languages gradually shift which suffixes they prefer for new generations.
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