A thousand years is also known as a ___________.

• Millennium (noun)
English Meaning: a period of 1000 years.
Bangla Meaning: সহস্রাব্দ; বর্ষসহস্রক; সবার জন্য অপরিমিত সুখসমৃদ্ধিপূর্ণ ভাবীকল; অনাগত স্বর্ণযুগ।

Complete Sentence: A thousand years is also known as a millennium.
- So, the correct spelling is Millennium (অপশন 'গ')

Example Sentence:
1. The construction of the ancient monument spanned over a millennium.
2. Advances in technology during the last millennium have transformed human society.

Source:
1. merriam-webster.
2. Accessible Dictionary by Bangla Academy.