prefix of reversal, deprivation, or removal (as in unhand, undo, unbutton), Old English on-, un-, from Proto-Germanic *andi- (source also of Old Saxon ant-, Old Norse and-, Dutch ont-, Old High German ant-, German ent-, Gothic and- "against"), from PIE *anti "facing opposite, near, in front of, before, against" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before").
More or less confused with un- (1) through similarity in the notions of "negation" and "reversal;" an adjective such as unlocked might represent "not locked" (un- (1)) or the past tense of unlock (un- (2)).
early 15c., "to sign at the bottom of a document," from Latin subscribere "write, write underneath, sign one's name; register," also figuratively "assent, agree to, approve," from sub "underneath" (see sub-) + scribere "to write" (from PIE root *skribh- "to cut"). The meaning "give one's consent" (by subscribing one's name) first recorded mid-15c.; that of "contribute money to" 1630s; and that of "become a regular buyer of a publication" 1711, all originally literal. Related: Subscribed; subscribing.
<a href="https://www.etymonline.com/word/unsubscribe">Etymology of unsubscribe by etymonline</a>
Harper, D. (n.d.). Etymology of unsubscribe. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/unsubscribe