See also s.v. šmt and etymological discussion s.v. $mt n.m.
The common use of this verb in Biblical Hebrew in the sense of "to destroy" demonstrates its common NW Semitic heritage, however the development into the concept of "excommunication" may be influenced by the Akkadian Št stem of emēdu "to get mixed up together", in this case, with the "other."
An extended discussion of this root is provided by Kottsieper in TDOT XVI:54ff.