Webster's Revised Unabridged Dictionary · 1913

Understand

Understand (un`dẽr*stand") , transitive verb

[Old English understanden, Anglo-Saxon understandan, literally, to stand under; compare Anglo-Saxon forstandan to understand, German verstehen. The development of sense is not clear. See Under, and Stand.]

1.
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. [Archaic]
Speaketh [i. e., speak thou] so plain at this time, I you pray, That we may understande what ye say. — Chaucer
I understand not what you mean by this. — Shakespeare
Understood not all was but a show. — Milton
A tongue not understanded of the people. — Bk. of Com. Prayer
2.
To be apprised, or have information, of; to learn; to be informed of; to hear; as, I understand that Congress has passed the bill.
3.
To recognize or hold as being or signifying; to suppose to mean; to interpret; to explain.
The most learned interpreters understood the words of sin, and not of Abel. — Locke
4.
To mean without expressing; to imply tacitly; to take for granted; to assume.
War, then, war, Open or understood, must be resolved. — Milton
5.
To stand under; to support. [Jocose & Rare] — Shakespeare
Collocations (2)
To give one to understand , to cause one to know.
To make one's self understood , to make one's meaning clear.

Understand , intransitive verb

1.
To have the use of the intellectual faculties; to be an intelligent being.
Imparadised in you, in whom alone I understand, and grow, and see. — Donne
2.
To be informed; to have or receive knowledge.
I came to Jerusalem, and understood of the evil that Eliashib did for Tobiah. — Neh. xiii. 7