To mash or crush something into a thick, soft pulp. Make sure you mush up that banana before you give it to Katie—she's still having trouble chewing solid food.

slang A foolish, idiotic person; someone lacking basic intelligence or common sense. Why they hired a mushhead like him to look after the accounts is beyond me! Oh God, look what I did—I've been such a mushhead today!

slang A person who is not able to speak clearly or properly. Often used humorously or hyperbolically. Sorry, I'm such a mushmouth today—I didn't sleep properly last night, and I'm finding it hard to get my words out the right way. I was kind of a mushmouth as a kid because of a slight speech impediment.