Why he had not attended the meeting is unknown to all. The underlined part is an example of -

• Why he had not attended the meeting is unknown to all. The underlined part is an example of - Noun clause.
• প্রশ্ন প্রদত্ত বাক্যে, প্রদত্ত বাক্যে 'Why he had not attended the meeting' clause টি subject হিসেবে বসাতে এটি Noun clause.

• A noun clause is a group of words that band together and act like a noun.
- Noun clauses are used when a single word isn't enough. They're always dependent clauses.

একটি বাক্যের বিভিন্ন স্থানে Noun clause বসতে পারে -
1. subject হিসাবে।
2. transitive verb এর object হিসেবে।
3. Linking verb এরপরে complement হিসাবে।
4. Preposition এরপরে।