The phrase "take the plunge" typically means to take a risk or make a bold decision. However, there are several antonyms (opposites) for this phrase that suggest caution or indecision. These could include "play it safe," "don't rock the boat," "procrastinate," "hesitate," or "avoid." While these alternatives may seem less adventurous, they can also reflect a thoughtful and deliberate approach to decision making. Depending on the situation, it may be wise to consider both the risks and benefits before taking the plunge, or to choose a more measured course of action instead.