Definition of understand :
1. To be apprised, or have information, of; to learn; to be informed of; to hear; as, I understand that Congress has passed the bill.
2. To be informed; to have or receive knowledge.
3. To have just and adequate ideas of; to apprehended the meaning or intention of; to have knowledge of; to comprehend; to know; as, to understand a problem in Euclid; to understand a proposition or a declaration; the court understands the advocate or his argument; to understand the sacred oracles; to understand a nod or a wink.
4. To have the use of the intellectual faculties; to be an intelligent being.
5. To mean without expressing; to imply tacitly; to take for granted; to assume.
6. To recognize or hold as being or signifying; to suppose to mean; to interpret; to explain.
7. To stand under; to support.
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believe (part of speech: verb)
learn (part of speech: verb)
know (part of speech: verb)