"Leap dark" can mean to take a gamble or make a risky decision without being fully informed. Synonyms for this phrase that convey the same sense of uncertainty include "jump in blind," "leap of faith," and "take a chance." Other phrases that express a similar sentiment include "throw caution to the wind," "trust your instincts," and "go out on a limb." All of these phrases convey the idea of taking a risk without having all the information, and the potential for both positive and negative outcomes. It's important to consider the risks and benefits before taking any action that could lead to a "leap dark" moment.