Wordnet 3.0
NOUN (2)
1. 
 son of Frederick William who in 1701 became the first king of Prussia (1657-1713); 
2. 
 Holy Roman Emperor from 1152 to 1190; 
 conceded supremacy to the pope; 
 drowned leading the Third Crusade (1123-1190); 
[syn: Frederick I, Frederick Barbarossa, Barbarossa]
WordNet (r) 3.0 (2006):
Frederick I
    n 1: son of Frederick William who in 1701 became the first king
         of Prussia (1657-1713)
    2: Holy Roman Emperor from 1152 to 1190; conceded supremacy to
       the pope; drowned leading the Third Crusade (1123-1190) [syn:
       Frederick I, Frederick Barbarossa, Barbarossa]