用作定语
▲～+n.
They agreed to hold an informal meeting.他们同意举行一次非正式的会议。
用作表语
▲S+be+～
The party will be informal, so you needn't dress up.这场聚会是非正式的,因此你不必盛装。
▲S+be+～+prep.-phrase
She is informal with everyone.她与所有的人打交道都不拘泥于礼节。
Her speech is informal and filled with colloquialism.她的演讲是非正式的,很口语化。