The word opposite can only be used when comparing two things or items and not when referring to a single thing or item. The meaning of opposite is a word expressing a meaning directly different or opposed to the meaning of another word. For example, the opposite of tall is short, therefore the opposite of the word advance or to advance is retreat or to retreat.
1 Additional Answer
The opposite of 'to advance' which means to move forward can either be; to withdraw, to retreat, to draw back, to recede, to pull back, to retire or move back.