a.[Z]

1. 未受命令的，未受指使的；自愿的
   He spoke out unbidden at the meeting.

   他在会议上主动发言。

2. 未被要求的，未被邀请的
   They arrived unbidden at the midnight.

   他们半夜里不期而至。

adj.

1. without having been invited.
2. arising without conscious effort.