Think of a large beetle at a window on a summer evening. It keeps going, it keeps bumping, it never quite gets where it wants to be, and the whole time there is a soft noise. That is the picture we can hold for bumble. Put a person in place of the beetle and nothing else changes: they are moving, they are trying, and they are knocking things over on the way. The word is soft because of that trying — it laughs a little, it does not accuse.
The supplied Wiktionary entries give two routes that meet in the same feeling. Etymology 1 calls bumble onomatopoeic and lines it up with bungle, jumble and fumble. Etymology 2 makes it a frequentative of boom or bum — the low buzzing an insect makes, which is also where bumblebee comes from. Sound and clumsiness sit together in the word from the start.
封包裡的 Wiktionary 給了兩條路，最後感覺卻很接近。第一條說 bumble 是擬聲字，並把它跟 bungle、jumble、fumble 排在一起。第二條說它是 boom 或 bum 的頻繁式，也就是昆蟲那種低低的嗡嗡聲——bumblebee 的 bumble 就是從這裡來的。可以想成：聲音的笨重和動作的笨拙，本來就長在同一個字裡。
Wiktionary entries (etymologies 1 and 2) supplied in this packet, source_refs kaikki:3f6f69a190036ae4:613459822 and kaikki:3f6f69a190036ae4:613466620
Two branches
身體上的笨拙：東撞西撞地動
這一族就是核心畫面本身：又動又撞，方向不太確定，但沒有停下來。
verb · B2
To move or do something in an unsteady, clumsy way — bumping into things, fumbling, getting small parts of it wrong — usually because you are lost, half asleep, or not very good at it yet.
笨拙地亂動亂闖
嘴上的笨拙：話繞來繞去講不清
同一種樣子換到嘴巴上：話也在動、也在撞、也到不了目的地。聽的人跟著繞了半天，還是沒抵達重點。
verb · B2
To talk in a confused, unclear way, so that people cannot follow what you mean — often going on and on without ever reaching the point.
講話含糊不清
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。
bumblenoun詞源 1/ˈbʌmbəl/
A confusion; a jumble.
bumbleverb詞源 1/ˈbʌmbəl/
To act or move in an awkward or confused manner (often clumsily, incompetently, or carelessly).
To carry out (a task) clumsily, incompetently, or with many careless mistakes; to bungle, to botch.
bumbleverb詞源 2/ˈbʌmbəl/
To boom, as a Eurasian bittern.
To buzz or bum.
To speak in a rambling, incoherent, or indistinct manner, especially at tedious length.
obsoleteTo grumble at; to blame.
bumblenoun詞源 2/ˈbʌmbəl/
A bumblebee.
dialectalA Eurasian bittern.
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。