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Definition of Frederick I
1. Noun. Son of Frederick William who in 1701 became the first king of Prussia (1657-1713). 
2. Noun. Holy Roman Emperor from 1152 to 1190; conceded supremacy to the pope; drowned leading the Third Crusade (1123-1190).
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1. Noun. Son of Frederick William who in 1701 became the first king of Prussia (1657-1713).