occurring or existing simultaneously or side by side

concurrent attacks by land, sea, and air.

acting in conjunction; cooperating

the concurrent efforts of several legislators to pass the new law.

having equal authority or jurisdiction

two concurrent courts of law.

accordant or agreeing

concurrent testimony by three witnesses.

tending to or intersecting at the same point

four concurrent lines.

something joint or contributory.

Archaic . a rival or competitor.

adverb

simultaneously , synchronously