Denshi Jisho — Online Japanese dictionary

けん 1: sphere; circle; range;
2: (Mathematical term) category (only in the context of "category theory")
Noun, Noun suffix 
けんがい outside range; outside orbit
Common word, Noun 
けんない within the sphere
Common word, Noun 
けんいき sphere (e.g. of knowledge, influence)
Noun 
けんこく cirque; corrie; cwm
Noun 
けんてん circle (for emphasis)
Noun 
けんろん category theory
Noun 

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