Full of fiends or demons; extremely wicked, cruel, or evil; characterized by devilish malevolence.
Compound of 'fiend' (Old English 'feond,' enemy or devil, from Proto-Germanic root meaning 'hating') and '-ful' suffix (Old English '-full,' full of). Archaic formation following the productive '-ful' pattern seen in 'hateful,' 'sinful,' 'dreadful.'
'Fiend' originally meant any enemy or hostile person, not necessarily a supernatural demon—it only acquired demonic associations later as Christian theology imported hell and devils into Anglo-Saxon worldviews.
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