The antonyms for the term "solemn oaths" could include frivolous promises, casual commitments, or lighthearted agreements. These phrases suggest a lack of seriousness, gravity, or trustworthiness in the promises made. The opposite of a solemn oath is an oath made impulsively or insincerely, without due consideration or intention to fulfill it. Thus, antonyms of solemn oaths connote a sense of unreliability, flippancy, or recklessness, and may be used to describe the opposite of the dignity, formality, or gravity that one associates with an oath.