亘こう古ここうこMeanings1nounfor ever; from ancient timesarchaicArchaic literary term meaning 'since antiquity' or 'eternally'. Not used in modern conversation; found in classical texts.古こ典てんでは「亘こう古こ」は永えい遠えんや太たい古こからの時じ間かんを表あらわす。