There are many synonyms for the phrase "have notion." Some of these synonyms include "understand," "comprehend," "grasp," "perceive," "discern," "apprehend," "know," "realize," and "identify." Each of these words carries slightly different connotations and shades of meaning, but they all refer to some form of understanding or awareness. Whether you have a deep understanding of a subject, a vague sense of something, or simply a passing familiarity with a topic, these synonyms can help you express your thoughts and ideas with greater precision and clarity. Knowing when and how to use each of these words can help you communicate more effectively with others and better navigate the complex world around us.