1630s, "occurring, living, or existing at the same time, belonging to the same age or period," from Medieval Latin contemporarius, from assimilated form of Latin com "with, together" (see con-) + temporarius "of time," from tempus "time, season, portion of time" (see temporal (adj.)). Form cotemporary was common in 18c. Meaning "modern, characteristic of the present" (in reference to art, literature, etc.) is from 1805.
"one who lives at the same time as another," 1630s, originally cotemporary, from co- + temporary; modified by influence of contemporary (adj.). A native word for it was time-fellow (1570s), and earlier was contemporanie (early 15c.), from Latin contemporaneus, used as a noun. Also compare crony.