formal

Please wear a suit and tie because the dinner at the embassy is formal.

(Chinese) 请穿西装打领带，因为大使馆的晚宴是很正式的。

He wrote a formal letter of complaint to the company's head office.

(Chinese) 他给公司总部写了一封正式的投诉信。

He learned Spanish from friends, but he has no formal language education.

(Chinese) 他是从朋友那里学西班牙语的，没有受过正规的语言教育。

The two countries finally signed a formal peace treaty after years of war.

(Chinese) 两国在多年的战争后终于签署了正式的和平条约。