noun which may take the genitive case particle 'no', noun
Honorific term for something strictly forbidden, often used in rules, traditions, or social contexts. Carries a formal or respectful tone.
この施設内での喫煙はご法度です。
Smoking is strictly prohibited within this facility.
彼の前でその話題はご法度だ。
That topic is taboo in front of him.
Combination of the honorific prefix ご (御) and 法度 (はっと), which originally referred to laws or prohibitions in the Edo period. The exact historical derivation of 法度 is uncertain, but it has long been used to denote strict rules.