You can think of sycamore as a name for a big shade tree rather than as the name of one species. The name started on a fig tree in Egypt, was handed to a European maple, and was handed again to the tall plane trees of North America. What the three trees share is size and deep shade, not family. So the first question a reader asks is not what is a sycamore, but who is writing, and where.
The Greek name sūkómoros means fig-mulberry: sûkon (fig) plus móron (mulberry). It named the Egyptian fig tree. English took it through Old French around 1350. In the 16th century it was applied to the European maple, and in the early 19th century to plane trees in North America, perhaps because they too give deep shade.
希臘文 sūkómoros 字面是「無花果桑樹」：sûkon（無花果）加 móron（桑樹），指的是埃及那種結果子的大樹。這個字大約在 1350 年前後經由古法文進入英文。十六世紀時被用在歐洲的槭樹上，十九世紀初又被用在北美的懸鈴木上，可能都是因為它們一樣樹大蔭濃。
Wiktionary entry for sycamore, supplied in this packet (kaikki extract, source_ref kaikki:3f6f69a190036ae4:815516968:24191).
Two branches
今天說 sycamore 時指的兩棵樹
這兩個意思是今天最常遇到的。它們都符合「大、寬葉、樹蔭濃」這個共同畫面，只是分別落在大西洋的兩邊。
noun · B2
A very large North American tree with broad leaves, whose bark peels off in flat pieces so that the trunk looks patched in cream, grey and brown; also the pale wood from this tree.
美國梧桐（懸鈴木）
這個名字最早指的那棵樹
這是名字的起點。它不是從上面那個畫面長出來的，反而是那個畫面的源頭：先有這棵埃及大樹，名字才被一路借走。
noun · C2
A large fig tree of Egypt and nearby countries that bears small fruit people can eat; this is the tree the name sycamore first belonged to.
埃及榕（西克莫無花果樹）