‘the simultaneous occurrence of events which appear significantly related but have no discernible causal connection: such synchronicity is quite staggering.’ From the Oxford Dictionary of English (ODE) on macOS

synchrony (another term for synchronicity)

‘1 simultaneous action, development, or occurrence. • the state of operating or developing according to the same time scale as something else: some individuals do not remain in synchrony with the twenty-four-hour day.’

‘1950s: coined (in sense 1) by Carl Jung.’