'Comment' comes from Latin 'comminisci' (to think up) — same root as 'mind' and 'mental.'
A verbal or written remark expressing an opinion or reaction; an explanatory or critical note on a text.
From Late Latin 'commentum' (interpretation, annotation), from Latin 'comminīscī' (to contrive, to devise, to think up), past participle 'commentus.' The verb is a compound of 'com-' (intensive prefix) and a root from PIE *men- (to think). The word thus literally means 'something thought up' or 'an invention of the mind
Julius Caesar's famous account of the Gallic Wars was titled 'Commentāriī dē Bellō Gallicō' — literally 'notes' or 'memoranda' about the Gallic War. Caesar used the word 'commentāriī' (plural of 'commentārius') to modestly suggest his work was mere rough notes rather than polished history, though it was in fact carefully crafted propaganda.