Antonyms for "more defining" might include "less defining," "vague," "ambiguous," "unclear," "indefinite," or "indeterminate." These words all suggest a lack of clarity or precision in definition. While "more defining" implies that something is becoming clearer or more specific, its antonyms suggest the opposite: that something is becoming more obscure or less well-defined. Depending on the context, any of these antonyms might be appropriate. For example, if someone is trying to clarify a point, they might use language that's more defining, whereas if they're intentionally trying to be vague or ambiguous, they might use words that are the antonyms of "more defining.