1794, "to write commentary upon," a back-formation from commentator. It unconsciously revived Middle English commentaten "write a commentary, expound a text" (early 15c.). But this oldest sense in English is rare. The main modern meaning "to deliver commentary" (on some public event) is attested from 1939 (implied in commentating). Related: Commentated.
commensalism
commensurable
commensurate
comment
commentary
commentate
commentation
commentator
commenter
commerce
commercial