Ad libitum is a Latin phrase meaning "at one's pleasure" or "at will." There are several synonyms for this phrase that can be used interchangeably in different contexts. One of the common synonyms is "freely" which means to do something without any constraints or limitations. Another synonym for ad libitum is "spontaneously" which implies doing something without prior planning or external influence. One can also use a synonym like "improvised" when referring to an action done impulsively without a specific plan. Other alternatives include "unrestricted" and "unlimited," which both suggest a sense of boundlessness or never-ending possibilities. All in all, there are several synonyms for ad libitum that can be used according to the context of usage.