Start with the press: apples go in, juice comes out, and someone has to decide what happens next. Leave the juice alone and it ferments into a drink with alcohol in it. Stop before that and you have a cloudy sweet juice. The word sits on that fork in the road, and which side you land on depends on where you are standing when you order it.
Wiktionary traces the word through Middle English sider and Old French sidre to Medieval Latin sicera, from Greek sikera and Hebrew shekhar, meaning a strong drink.
字源資料把這個字一路追到中古英文 sider、古法文 sidre、中世紀拉丁文 sīcera，再到希臘文 σίκερα 和希伯來文 שֵׁכָר，原意是「烈性的飲料」。所以含酒精的那一支，其實是這個字最老的那條路。
Wiktionary entry for cider, supplied in packet (source_ref kaikki:3f6f69a190036ae4:574773002)
Three branches
發酵過的那一邊
岔路往發酵走：糖變成酒精，這杯就成了酒。
noun · B1
In British English, a drink made by letting apple juice ferment, so that it contains alcohol; also one glass or bottle of that drink. The same word covers drinks made this way from other fruit, such as pears.
蘋果酒
沒有發酵的那一邊
岔路在發酵前停住：剩下的是混濁的鮮榨果汁。
noun · B1
In American English, a cloudy drink made from freshly pressed apples, with no alcohol in it; the apple pulp is left in, so it looks thicker and darker than clear apple juice.
蘋果汁（美式，不含酒精）
名字傳出去以後
這一支名字跟核心畫面同源，東西卻換了：既不是蘋果做的，也沒有酒精。
noun · B2
In Japan and South Korea, a clear, sweet, fizzy soft drink with a lemon-lime taste, sold under this English name; it has no alcohol and is not made from apples.
汽水（日韓用法）