The synonym of the word 'Expand' is-

The correct answer is: খ) Increase.

Increase:
- Bangla meaning: to become progressively greater (as in size, amount, number, or intensity)
- English meaning: বৃদ্ধি; প্রবৃদ্ধি; উপচয়; বাড়।

Expand:
- Bangla meaning: প্রসারিত করা বা হওয়া।
- English meaning: to increase the extent, number, volume, or scope of : enlarge.

Other options:
ক) Destroy
- Bangla meaning:ধ্বংস; নষ্ট; বিধ্বস্ত; বরবাদ; পয়মাল করা।
- English meaning: to ruin the structure, organic existence, or condition of

গ) Segment
- Bangla meaning: কর্তিতাংশ; ছিন্নাংশ
- English meaning: a portion cut off from a geometric figure by one or more points, lines, or planes

ঘ) Calm
- Bangla meaning: শান্ত; নির্বাত; স্থির; শান্ত; নিস্তরঙ্গ।
- English meaning: a period or condition of freedom from storms, high winds, or rough activity of water

Source:
1. Merriam-Webster dictionary.
2. Accessible Dictionary.
3. Cambridge Dictionary.