ひでん
secret (recipe, medicine, etc.); mysteries (e.g. of an art)
Noun, No-adjective
内弟子うちでしとは師しと寝食しんしょくをともにし、あらゆる武術ぶじゅつのノウハウと秘伝ひでんを伝つたえる制度せいどだ。
Apprenticeship is a system where you eat, sleep and live with your master and are taught various martial arts know-how and secrets.