From the given options choose the one which is opposite in meaning to the word given below 

GAIN

Lose

The word that is opposite in meaning to gain is lose.

• Gain means to obtain or acquire something, especially after effort.
• Lose means to fail to keep or obtain something, especially after having it.

The other options are not opposites of gain.

• Grow means to increase in size or amount.
• Increase means to become greater in size, amount, or intensity.
• Expand means to become larger or more extensive.