ascertain

from The American Heritage® Dictionary of the English Language, 5th Edition.

• transitive verb To discover with certainty, as through examination or experimentation. synonym: discover.
• transitive verb Archaic To make certain, definite, and precise.

from The Century Dictionary.

• To make certain; determine; define or reduce to precision by removing doubt, obscurity, or ambiguity; establish; prove.
• To find out by trial, examination, or experiment, so as to know as certain; acquire an accurate knowledge of: as, to ascertain the weight of a commodity or the purity of a metal.
• To make sure of; insure.
• To make certain or sure; certify; assure; inform.
• To establish with certainty; render invariable, or not subject to caprice; fix.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb obsolete To render (a person) certain; to cause to feel certain; to make confident; to assure; to apprise.
• transitive verb Archaic To make (a thing) certain to the mind; to free from obscurity, doubt, or change; to make sure of; to fix; to determine.
• transitive verb To find out or learn for a certainty, by trial, examination, or experiment; to get to know.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb To find out definitely; to discover or establish.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb find out, learn, or determine with certainty, usually by making an inquiry or other effort
• verb establish after a calculation, investigation, experiment, survey, or study
• verb be careful or certain to do something; make certain of something
• verb learn or discover with certainty