parallel

Definition

Extending or moving in the same direction, but never meeting or intersecting

The two roads ran parallel to each other for miles, separated by a narrow strip of land.

Similar or equivalent in some way, often used to describe situations or processes

The company is running a parallel investigation into the cause of the accident, separate from the official inquiry.

concurrentOften implies happening at the same time, whereas parallel can also describe things that are similar but not simultaneous simultaneousEmphasizes the idea of things happening or existing at the same time, often in a coordinated way analogousSuggests a similarity or equivalence between things, but often in a more abstract or theoretical sense