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Whereof means 'of which' or 'of what'. It points back to something already named and shows that the next part belongs to it or is about it: 'the matters whereof he spoke' = 'the matters that he spoke of'; 'a country whereof little is known' = 'a country of which little is known'.
Whereof means 'of which' or 'of what'Whereof的意思是「of which關於哪個」或「of what關於什麼」。It points back to something already named它指回前面已經提過的東西，and shows that the next part belongs to it or is about it表示接下來的部分是屬於它或跟它有關：'the matters whereof he spoke' = 'the matters that he spoke of'像「the matters whereof he spoke他所說的那些事」等於「the matters that he spoke of」；'a country whereof little is known' = 'a country of which little is known'「a country whereof little is known人們對它所知甚少的一個國家」等於「a country of which little is known」。
It can also, more rarely, ask: 'Whereof do you accuse me?' Of all the where- words this is the deadest in ordinary speech.
It can also, more rarely, ask它也可以，比較少見地，用來提問：'Whereof do you accuse me?'像「Whereof do you accuse me你指控我什麼？」Of all the where- words在所有where-開頭的字裡，this is the deadest in ordinary speech這是日常口語裡死得最徹底的一個。
You will find it in the Bible, in Shakespeare, in old contracts and wills, and in the closing formula of formal legal documents: 'In witness whereof, the parties have signed…' — that phrase is still printed on real contracts today, so it is the one place a modern person actually meets it.
You will find it in the Bible, in Shakespeare, in old contracts and wills你會在聖經、莎士比亞、還有老式合約和遺囑裡看到它，and in the closing formula of formal legal documents還有正式法律文件結尾的固定句裡：'In witness whereof, the parties have signed…'像「In witness whereof, the parties have signed…茲證明如上，雙方特此簽署……」——that phrase is still printed on real contracts today這句話現在真實合約上還印著，so it is the one place a modern person actually meets it所以這是現代人真正會碰到這個字的地方。
Philosophy quotes it too, in the famous translated line 'Whereof one cannot speak, thereof one must be silent.' Nobody uses it in speech; even formal modern writing prefers 'of which'.
Philosophy quotes it too哲學裡也會引用它，in the famous translated line在那句有名的翻譯名言裡：'Whereof one cannot speak, thereof one must be silent.'「Whereof one cannot speak, thereof one must be silent對於不能說的事，就應該保持沉默」。Nobody uses it in speech沒有人會在講話時用它，even formal modern writing prefers 'of which'就連正式的現代寫作也比較喜歡用「of which」。
組成where (which, what) + of. Built exactly like whereby and wherein; Swedish varav and Dutch waaraf are made the same way, which shows how old the habit is.
原始詞典資料6 筆記錄
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。
whereofconj/wɛəɹˈɒv/
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formalOf what.
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formalOf which.
- SATURNINUS: Go fetch them hither to us presently. TITUS: Why, there they are, both baked in that pie, Whereof their mother daintily hath fed, Eating the flesh that she herself hath bred.
- However, upon a ſtrict Review, I blotted out ſeveral Paſſages of leſs Moment which were in my firſt Copy, for fear of being cenſured as tedious and trifling, whereof Travellers are often, perhaps not without Juſtice, accuſed.
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formalOf whom.
- Now one day of the days, […] the Sultan cast his eyes upon her as she stood before him, and said to his Grand Wazir, “This be the very woman whereof I spake to thee yesterday, so do thou straightway bring her before me, that I may see what be her suit and fulfil her need.”
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archaicWith or by which.
whereofadv/wɛəɹˈɒv/
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archaicOf what.
- Anthonio. [I]n ſooth I know not why I am ſo ſad, It wearies me: you ſay it wearies you; But how I caught it, found it, or came by it, What ſtuffe ’tis made of, whereof it is borne, I am to learne: and ſuch a Want-wit ſadnesse makes of mee, That I haue much ado to know my ſelfe.
- Whereof one cannot speak, thereof one must be silent.
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archaicOf which.
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。