commentator n.

late 14c., "explanation, spoken or written remark," from Old French coment "commentary" or directly from Late Latin commentum "comment, interpretation," in classical Latin "invention, fabrication, fiction," neuter past participle of comminisci "to contrive, devise," from com-, here perhaps an intensive prefix (see com-), + base of meminisse "to remember," related to mens (genitive mentis) "mind" (from PIE root *men- (1) "to think").

The Latin word meaning "something invented" was taken by Isidore and other Christian theologians for "interpretation, annotation." No comment as a stock refusal to answer a journalist's question is first recorded 1950, from Truman's White House press secretary Charles Ross.

early 15c., "series or collection of comments," from Medieval Latin commentarius "notebook, annotation; diary, memoir," noun use of adjective, "relating to comments," from Late Latin commentum "comment, interpretation" (see comment (n.)). Perhaps the Medieval Latin noun is short for volumen commentarium. Especially "explanation of difficult and obscure passages in a book or other writing" (1530s). Meaning "historical narrative" is from c. 1600. Meaning "description of some public event" is from 1927.

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.