na-adjective
extremely rude; terribly impolite
A strong, formal yojijukugo used to describe or apologize for extreme rudeness. Often used in set phrases like 失礼千万な態度 or 失礼千万で申し訳ありません.
彼の失礼千万な態度に、皆が呆れた。
Everyone was appalled by his extremely rude attitude.
失礼千万で申し訳ありませんでした。
I am terribly sorry for my extreme rudeness.
A yojijukugo combining 失礼 (rudeness) and 千万 (ten million, here meaning 'extremely'). The exact historical derivation is uncertain, but it follows a common pattern of intensifying a noun with 千万.