順著旁邊掉進來
兩個意思共用同一個畫面，差別只在「掉進來的」是一件事，還是一句話。
as an unplanned result · r · C1
In a way that was not planned, but that happened as a result of something else you were doing.
附帶地
核心畫面
A useful picture: something falls in beside the main thing rather than being the main thing. You were doing one job, and this other bit came along on the side — not planned, not central, just riding along.
主線在走，而有樣東西「順著旁邊掉進來」——它不是你原本要做的那件事，是跟著那件事一起發生的。像走路時鞋底黏到一片葉子…更多收起
主線在走，而有樣東西「順著旁邊掉進來」——它不是你原本要做的那件事，是跟著那件事一起發生的。像走路時鞋底黏到一片葉子：你不是為了撿葉子才出門，但葉子確實跟著回來了。這個「不是主角、只是順著旁邊來」的感覺，同時解釋了它講事情時的「附帶」，也解釋了它講話時的「順便一提」。From the word’s history
From incidental + -ly; incident goes back to Latin incidere 'to fall upon, fall into' (in- 'on' + cadere 'to fall').
incidentally 是 incidental 加上副詞的 -ly。往上追，incident 來自拉丁文 incidere「掉到…上面、落進來」（in-「進、上」+ cadere「掉落」）。「掉進來」這個動作正是核心畫面的來源：事情不是被安排進來的，是自己落進來的。
Latin incidere (in- + cadere 'to fall'), via incident / incidental — standard etymological dictionaries of English
One branch
原始詞典資料3 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
incidentallyadv/ˌɪnsɪˈdɛntl̩i/
- 1
mannerIn an incidental manner.
- Near-synonyms: coincidentally, happenstantially, circumstantially, by chance, accidentally, semirandomly, randomly
- 2
mannerIn an incidental manner.
- Near-synonym: in passing
- The book discussed the subject, but only incidentally.
- 3
mannerIn an incidental manner.
- Incidentally, did you hear anything new from your brother yesterday?
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。