'angriest' originates from English formation: the adjective 'angry' plus the superlative suffix '-est', where '-est' meant 'most' or 'to the highest degree'; 'angry' ultimately traces to Old Norse 'angr' meaning 'grief, sorrow, distress' and to the PIE root 'angh-' ('tight, painful').

'angry' came through Middle English 'angry/angri' from Old Norse 'angrigr' (from 'angr' “grief; distress”), and the Old English superlative suffix '-est' (from Proto-Germanic '-ista-') was added to form the modern English word 'angriest'.

Initially, related forms of 'angry' carried the sense 'afflicted; sorrowful; distressed'; over time the sense shifted to 'irate', so 'angriest' now means 'most angry'.