The antonyms for the word "under rating" are "overrating," "praising," and "overestimating." Overrating means to give undue importance or value to something, which in this context means that the thing is rated higher than it deserves. Praising means to express admiration or approval for someone or something, which is the opposite of under rating. Overestimating means to estimate too high, which is the opposite of underestimating. All of these words suggest that whatever is being rated or evaluated is being given too much credit, attention, or consideration, and that a more accurate assessment is necessary.