Old English 'dom' meant 'judgment,' not ruin — it darkened through association with the Last Judgment's final sentencing.
Death, destruction, or an unavoidable terrible fate; historically, a judgment or decree.
From Old English 'dōm' (judgment, law, decree, authority), from Proto-Germanic '*dōmaz' (judgment, statute), from PIE *dʰeh₁- (to set, to put, to place). The original meaning was entirely neutral — a 'doom' was a formal judgment or legal decision. The 'Domesday Book' (1086) is literally the 'Book of Judgment.' The shift toward 'ruin, destruction' occurred