從騎的東西上下來
這一組用的是畫面的前半：人自己從上面下來。
verb · B2
To get down off a horse, bicycle or motorbike that you are sitting on.
下馬、下車（從騎的東西上下來）
核心畫面
Something was up on top of something else and held there — a rider on a horse, a camera on a tripod, a disk inside a system. Dismount is the undoing of that: it comes back down, and the support lets go. The picture always has two halves, the coming down and the release, and different uses of the word lean on different halves.
可以想成有個東西本來在另一個東西上面，而且被固定在那裡。可能是人坐在馬背上，可能是相機架在腳架上，也可能是磁碟接在系…更多收起
可以想成有個東西本來在另一個東西上面，而且被固定在那裡。可能是人坐在馬背上，可能是相機架在腳架上，也可能是磁碟接在系統裡。dismount 就是把這件事倒回來：東西下來了，架著它的那一邊也放手了。這個畫面有兩半——下來，和放手——不同的用法靠的是不同那一半。From the word’s history
The word is dis- (undo, reverse) plus mount (to climb up onto something). Probably taken straight over from Old French desmonter. So the reversal is built into the word itself: whatever was mounted comes back down.
這個字是 dis-（解除、反過來）加上 mount（爬上去、架上去）。可能是照著古法文 desmonter 直接搬過來的。所以「倒回來」這件事就寫在字裡面：原本被 mount 上去的，現在下來了。
Wiktionary entry for dismount (kaikki:3f6f69a190036ae4:510038219): From dis- + mount, probably a calque of Old French desmonter.
Two branches
把裝上去的東西取下
這一組用的是畫面的後半：架子放手，東西鬆開。
verb · C1
To take something out of the base, frame or stand that holds it — a gun off its stand, a camera off a tripod, a screen off a wall bracket.
卸下、拆下（從支架上）