一、这棵树的结构1. How the tree is built

树根是原始印欧语（PIE，约 6000 年前，带 * 的都是构拟形）。往上分 10 条语义大枝（身体、生命、心智……），每条枝上长着若干熟词词族——heart、foot、two 这些你早就认识的词是免费的记忆锚点。点开词族能看到音变链（这个词怎么走到今天）、音变规律、记忆钩子，以及一把彩色叶子——每片叶子是一个同族词，颜色标语源：The root of the tree is Proto-Indo-European (PIE, roughly 6,000 years ago; everything marked with * is a reconstructed form). Above it the tree divides into 10 semantic boughs (body, life, mind…), and on each bough grow a number of familiar-word families — heart, foot, two and the like are words you already know, so they come free as memory anchors. Open a family and you get its sound-change chain (how the word travelled to the present day), the sound law at work, a memory hook, and a handful of coloured leaves — each leaf a member of the family, coloured by its source:

点开任何一片叶子，还有逐词素拆解：前缀蓝、词根红、后缀绿（标明名词尾/形容词尾/副词尾等词性）、连接灰——整个词像积木一样摊开，配一句该词专属的记忆钩子（字面义 → 引申义）。刷题答完每张卡也会展示拆解。Open any leaf and you also get a morpheme-by-morpheme breakdown: prefix in blue, root in red, suffix in green (labelled as noun / adjective / adverb ending and so on), connector in grey — the whole word laid out like building blocks, with a memory hook written for that word alone (literal sense → extended sense). Every flashcard shows the same breakdown once you have answered.

二、闪卡就长在树上2. The flashcards grow on the tree

1. 点任何一片叶子：看详情，点「✎ 考我这个词」立刻单词速测——这时单词与拆解会被模糊遮住，免得照着抄；再点一次收起，恢复正常显示。Click any leaf for its details, then hit "✎ Quiz me on this word" for an instant single-word test — the word and its breakdown are blurred out while you answer, so you cannot simply copy them; click the button again to close the test and restore the normal view.
2. 点词族 / 大枝上的 🃏：开右侧刷题面板，按范围连续刷。Click the 🃏 on a family or a bough to open the drill panel on the right and work through that scope without stopping.
3. 同一个词答对一次即记为掌握——叶子当场点亮 ✓，顶栏进度 +1。答错的词本轮内会自动再排队，等会儿再撞见一次。Getting a word right once marks it as mastered — the leaf lights up with a ✓ on the spot and the progress bar ticks up by one. Words you get wrong are queued again within the same round, so you will meet them once more before it ends.
4. 进度只存在页面内存里：关页前点右上「💾 存档」导出，下次导入续上。Progress lives only in the page's memory: hit "💾 Save" at the top right and export before you close the tab, then import it next time to pick up where you left off.

三、格林定律速查表（英语土词和拉丁词为什么长得像又不像）3. The Grimm's law cheat sheet (why native English words and Latin ones look alike, and yet not quite)

公元前一千年左右，日耳曼语（英语的祖先）的塞音整体挪了一位；拉丁、希腊没挪。先记 p↔f、t↔th、k↔h、d↔t 四条，覆盖本树七成例子。每个词族的「音变规律」栏会告诉你那一族用的是哪条。Around 1000 BC the stops of Germanic — the ancestor of English — all shifted one notch; Latin and Greek did not shift. Learn the four pairs p↔f, t↔th, k↔h, d↔t first and you cover seven out of ten examples in this tree. Each family's "sound law" panel tells you which rule that family runs on.

另两条常用的非格林规律：希腊语把词首 s- 读成 h-（salt/hals · sub/hypo · super/hyper · semi/hemi），把词首 w- 丢掉（work/ergon · wise/idea）。Two more handy rules that are not Grimm's: Greek turns initial s- into h- (salt/hals · sub/hypo · super/hyper · semi/hemi), and drops initial w- altogether (work/ergon · wise/idea).

四、Etymonline 一分钟用法4. Etymonline in one minute

1. 到 etymonline.com 查词（免费无需登录），沿着 from … from … 一路读到最底下的 from PIE root *xxx-。Look the word up at etymonline.com (free, no login), and follow the from … from … chain all the way down to from PIE root *xxx- at the bottom.
2. 点进词根页，看 It forms all or part of: ——那就是同族词表，对应这里的一个词族。Click through to the root's own page and look at It forms all or part of: — that is the family list, and it corresponds to one word family here.
3. 斜体是外语原词，后面引号里是它的意思；带 * 号＝构拟形；「of uncertain origin」＝来源不明，别硬编故事。Italics are the foreign source word and the quotation marks after it give its sense; a * marks a reconstructed form; "of uncertain origin" means exactly that — do not invent a story to fill the gap.
4. 每片叶子的弹窗里都有 Etymonline 直达链接——可以怀疑这棵树，但请点开核对。Every leaf's popup carries a direct Etymonline link — you are welcome to doubt this tree, but please click through and check.