gatepost
noun [ C ] uk/ˈɡeɪt.pəʊst/ us/ˈɡeɪt.poʊst/
（大门的）门柱
a post to which a gate is fixed, or to which it fastens when closed
Idiom
between you, me, and the gatepostidiom informal (also between you, me, and the bedpost) “你我私下说说”，“不要告诉别人”（用于表达希望对话不要外泄）
an expression used to tell someone that what you are about to say should be kept secret