Contemporary, contemporaneous, coeval, coetaneous, synchronous, simultaneous, coincident, concomitant, concurrent are comparable when they mean existing, living, or occurring at the same time.
In contemporary and contemporaneous (of which contemporary is applied somewhat more frequently to persons, contemporaneous to events), the time regarding which agreement is implied is determined only through the context.
Contemporary, but not contemporaneous, may imply reference to the present; it then means of the same time as that of the speaker or writer.
Coeval usually implies contemporaneousness for a long time or at a remote time.
Coetaneous is a close synonym of coeval, but it may more specifically suggest contemporaneity of origin.
Synchronous implies an exact correspondence between the usually brief periods of time involved; simultaneous more frequently denotes agreement in the same point or instant of time.
Coincident applies to events that are regarded as falling or happening at the same time; it ordinarily minimizes the notion of causal relation.
Concomitant carries so strong an implication of attendance or association that it often imputes a subordinate character; however, only when it implies coincidence or synchronousness is it truly a synonym of the other words.
Concurrent adds to synchronous the implication of parallelism or agreement.