The synonym of 'isolation' is-

The synonym of 'isolation' is detachment.

Here's a breakdown of the other options:

• Entertainment: This is a form of amusement or enjoyment.

• Fierce: This means fierce or intense.

• Acquaintance: This refers to a person you know but are not close to.

Therefore, detachment is the most appropriate synonym for 'isolation'. It means the state of being separated or alone.