Underestimate: they are better than you expected. Undermine: someone tries to cause your efforts to fail in a subtle way. Hope this helps :)

I agree with the others. It might help to understand the origins of UNDERMINE. When attacking an enemy castle, one might dig a tunnel (aka a mine) under the wall, or a tower, then burn the supporting wooden beams, causing the wall to fall down. Underestimate just means you didn't realize how good something was.

Yes what they said below! Good explanations. "Undermine" for me has the meaning of "sabotage" however in a more subtle way. Example: He undermined John's chances to win the election by not supporting him with enough funds and giving him false information about his opponent.

Hello, Underestimate means that you thought something was going to be or do worse or less than it was. If you thought your football team was going to win the match, but they actually won, you could say "I underestimated the team's chances of winning." If you thought a candy bar costs $1 but it really costs $2, you could say "I underestimated the price of the candy bar." To undermine means to lessen the effectiveness/power/ability. If a student did not listen to the teacher in class, the teacher could say, "Stop undermining my authority." Someone who cheats on a test is undermining their education. Undermine has a somewhat negative connotation. Thank you! Kathleen

Underestimate means you assume something has less of a quality than what it actually has. Undermine means to meddle and get in the way of someone's well laid out plans.