—v.t. 1. to perceive the meaning of; grasp the idea of; comprehend: to understand Spanish; I didn't understand your question. 2. to be thoroughly familiar with; apprehend clearly the character, nature, or subtleties of: to understand a trade. 3. to assign a meaning to; interpret: He understood her suggestion as a complaint. 4. to grasp the significance, implications, or importance of: He does not understand responsibility. 5. to regard as firmly communicated; take as agreed or settled: I understand that you will repay this loan in 30 days. 6. to learn or hear: I understand that you are going out of town. 7. to accept as true; believe: I understand that you are trying to be truthful, but you are wrong. 8. to construe in a particular way: You are to understand the phrase literally. 9. to supply mentally (something that is not expressed).
—v.i. 1. to perceive what is meant; grasp the information conveyed: She told them about it in simple words, hoping they would understand. 2. to accept tolerantly or sympathetically: If you can't do it, I'll understand. 3. to have knowledge or background, as on a particular subject: He understands about boats. 4. to have a systematic interpretation or rationale, as in a field or area of knowledge: He can repeat every rule in the book, but he just doesn't understand.