形容詞 apropos:

1. of an appropriate or pertinent nature

副詞 apropos:

1. by the way
   同義詞：incidentally
2. at an opportune time
   同義詞：seasonably, timely, well-timed

1. Apropos, I have something to tell you.
   順便，我有點事跟你說。
2. Apropos our date for lunch, I can't go.
   關于我們的午餐約會，我不能去
3. Apropos of what you were just saying ...
   關於你剛才所說的話 ...

ap.ro.pos

adj.（形容詞）
Being at once opportune and to the point.See Synonyms at relevant
恰當的：適宜而切題的參見 relevant
adv.（副詞）
At an appropriate time; opportunely.
適宜地：在合適時間地；適宜地
By the way; incidentally:
順便說；隨帶問一句：
例句：
Apropos, where were you yesterdayô
順便問一句，你昨天在哪兒ô

prep.（介詞）
With regard to; concerning:
關于；有關：
例句：
Apropos our date for lunch, I can`t go.
關于我們的午餐約會，我不能去

來源：
French à propos
法語 à propos
à [to] from Latin ad- * see ad-
à [到] 源自 拉丁語 ad- *參見 ad-
propos [purpose] from Latin prôpositum from prôponere prôposit- [to intend] * see propose
propos [目的] 源自 拉丁語 prôpositum 源自 prôponere prôposit- [傾向于] *參見 propose