極める
きわめる to carry to extremes to go to the end of something to investigate thoroughly to master

極め付き
きわめつき guaranteed

極め付きの品
きわめつきのしな article of certified genuineness

極め尽くす
きわめつくす to do thoroughly to check through and through

極め所
きめどころ crucial point perfect chance

極め手
きめて decisive factor person who decides