Greek also had an alpha copulativum, a- or ha-, expressing union or likeness, which is the a- expressing "together" in acolyte, acoustic, Adelphi, etc. It is from PIE root *sem- (1) "one; as one, together with."
1660s, "existing or happening at the same time," from Late Latin synchronus "simultaneous," from Greek synkhronos "happening at the same time," from syn- "together" (see syn-) + khronos "time" (see chrono-). Meaning "recurring at the same successive instants of time" is attested from 1670s. Related: Synchronously.
<a href="https://www.etymonline.com/word/asynchronous">Etymology of asynchronous by etymonline</a>
Harper, D. (n.d.). Etymology of asynchronous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/asynchronous