concurrent

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

• adjective Happening, existing, or done at the same time as something else: synonym: contemporary.
• adjective Meeting or tending to meet at the same point; convergent.
• adjective Being in accordance; harmonious.

from The Century Dictionary.

• Meeting in a point; passing through a common point.
• Concurring, or acting in conjunction; agreeing in the same act; contributing to the same event or effect; operating with; coincident.
• Conjoined; joint; concomitant; cördinate; combined.
• noun One who concurs; one agreeing with or like another in opinion, action, occupation, etc.
• noun In English law, specifically, one who accompanies a sheriff's officer as witness or assistant.
• noun That which concurs; a joint or contributory thing.
• noun One having an equal claim or joint right.
• noun A rival claimant or opponent; a competitor.
• noun The day, or in the case of leap-year the two days, required to be added to fifty-two weeks to make the civil year correspond with the solar: so called because they concur with the solar cycle, whose course they follow.

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

• noun One who, or that which, concurs; a joint or contributory cause.
• noun One pursuing the same course, or seeking the same objects; hence, a rival; an opponent.
• noun (Chron.) One of the supernumerary days of the year over fifty-two complete weeks; -- so called because they concur with the solar cycle, the course of which they follow.
• adjective Acting in conjunction; agreeing in the same act or opinion; contributing to the same event or effect; coöperating.
• adjective Conjoined; associate; concomitant; existing or happening at the same time.
• adjective Joint and equal in authority; taking cognizance of similar questions; operating on the same objects.
• adjective (Geom.) Meeting in one point.

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

• adjective Happening at the same time; simultaneous.
• adjective Belonging to the same period; contemporary.
• adjective Running alongside one another on parallel courses; moving together in space.
• adjective computing Involving more than one thread of computation.
• noun One who, or that which, concurs; a joint or contributory cause.
• noun One pursuing the same course, or seeking the same objects; hence, a rival; an opponent.
• noun One of the supernumerary days of the year over fifty-two complete weeks; so called because they concur with the solar cycle, the course of which they follow.

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

• adjective occurring or operating at the same time